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Old 05-25-2020, 06:38 PM   #1
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6 spd. Allison trans ?

I have a 2020 Silverado 2500hd 6.6 gasser with the 6 sd Allison. For towing/hauling how do you use the 6 sd Allison? What gear, tow/haul mod? Use manual or just put it D and go? I pull a Puma 295BHSSOK. First time pulling with this truck. The 2003 Silverado 6.0 gas with4 sd trans. Never used tow mod, shifted too soon and stayed too long before up shift. Ran 4th gear unless it shifted a lot, then went to 3rd gear. It had 4.10 gears and 2020 has 3.73 gearing.
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Old 05-26-2020, 08:12 AM   #2
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I would put it in drive, tow/haul mode, and go. The truck, and engine/tranny combo is designed to tow. Tow/haul mode in any truck will cause the tranny to maybe shift a little early, and/or late. It is trying to keep the engine in the best torque band for towing.

A number of people will tell you to lock out 6th gear, do this or that, but Chevy designed and programmed the truck to be put in "drive", tow/haul, and tow anywhere all the way up to the max weight. I always figured they know a bit more than I do, and that is what I have always done without any issues in the Sierra's, Rockies...etc.
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Old 05-26-2020, 08:28 AM   #3
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I would put it in drive, tow/haul mode, and go. The truck, and engine/tranny combo is designed to tow. Tow/haul mode in any truck will cause the tranny to maybe shift a little early, and/or late. It is trying to keep the engine in the best torque band for towing.

A number of people will tell you to lock out 6th gear, do this or that, but Chevy designed and programmed the truck to be put in "drive", tow/haul, and tow anywhere all the way up to the max weight. I always figured they know a bit more than I do, and that is what I have always done without any issues in the Sierra's, Rockies...etc.
I agree with this advice.

Are you sure your transmission is an Allison? I thought the diesel version had an Allison but that the gasser had a GM 6 spd.
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Old 05-26-2020, 08:34 AM   #4
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I would suggest reading the owners manual. I've also seen separate towing manuals, either paper or online.
When I tow, I put my old 6 speed Allison in tow/haul and D, and usually use cruise control.
I don't like the shift response when braking going downhill, so then I will put it in manual and use the +/- to shift manually.
After a few trips I'm sure you will get the hang of yours.
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Old 05-26-2020, 08:51 AM   #5
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Hi,

I have the six speed Allison in my current Duramax; I just hit tow haul and forget it. Same way on my 2009 Duramax -- set it and forget it.

And yes, I wasn't aware the Allison six speed was available in the gassers.

FWIW.

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Old 05-26-2020, 09:54 AM   #6
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Yes, I am sure. Gasses have had the Allison starting in 2006.
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Old 05-26-2020, 10:04 AM   #7
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Yes, I am sure. Gasses have had the Allison starting in 2006.

From the Chevrolet website:


Diesels have a 10-speed Allison
  • 445 hp [332 kW] @ 2800 rpm
  • 910 b-ft. of torque [1220 Nm] @ 1600 rpm
  • 3.42 rear axle ratio
  • Exhaust brake
  • Engine block heater
  • Capped fuel fill
  • Paired with an Allison® 10-speed automatic transmission
  • Diesel Exhaust Fluid (DEF) fill located in fuel door
  • Engine after run feature for cooling performance
  • May require additional optional equipment
Gassers have a 6-spd GM tranny
  • 401 hp [299 kW] @ 5200 rpm
  • 464 lb-ft of torque [629 N-m] @ 4000 rpm
  • 3.73 rear axle ratio
  • Paired with a 6-speed automatic transmission
  • Capless fuel fill
EDIT:

from the GM-Trucks.com forum:
"Technical powertrain discussion specifically for the 2020+ L8T 6.6L Gas V8 engine and MYD 6-Speed HD transmission combination on the 2020 Chevrolet Silverado 2500 / 3500 or 2020 GMC Sierra 2500 / 3500"
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Old 05-26-2020, 10:12 AM   #8
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Yes, I am sure. Gasses have had the Allison starting in 2006.
you have the 6L90 just as bullet proof as the older 4L80 . mo allison in the gassers but the chevy tranny is great
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Old 05-26-2020, 10:12 AM   #9
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Hi,

Six speed, yes, but not an Allison. Here is the link.

https://media.chevrolet.com/media/us...o-hd-2020.html

FWIW.

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Old 05-26-2020, 10:13 AM   #10
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Originally Posted by RRSCOTT View Post
I have a 2020 Silverado 2500hd 6.6 gasser with the 6 sd Allison. For towing/hauling how do you use the 6 sd Allison? [...]
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Originally Posted by RRSCOTT View Post
Yes, I am sure. Gasses have had the Allison starting in 2006.
You have the GM 6L90 transmission in your 2020 Silverado 2500 6.6L gasoline V8.

As for modes, the best advice is given above. Read the manual, try the settings, adjust as you drive, and find your sweet spot. I'm still tinkering with my favorite combination of tow/haul settings. It's part of the fun.
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Old 05-26-2020, 10:15 AM   #11
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GM 6L90 MYD transmission:

https://gmauthority.com/blog/gm/gm-transmissions/myd/
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Old 05-26-2020, 03:43 PM   #12
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The answer to the question is: TOW/HAUL.
I, TOW/HAUL it, put it in D, and go. Set the Cruise Control to 65 where allowed. Adjust speed for hills and or mountains.
Happy Trails. Be safe out there.
P/S
TOW/HAUL Mode lowers the pressures in the transmission allowing it to run cooler, thus, adding life to it and the fluids. Most overheating of tow vehicles comes from the transmission, adding hot fluids to be cooled by the system.
And, like the big trucks up hill, slow down the ground speed, but keep the RPMs up.
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Old 05-26-2020, 09:15 PM   #13
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Sometimes letting it go into 6th isn't the best. On my older Duramax, yes it would pull the trailer fine in 6th at 1700 rpm, but I got better fuel mileage by locking it into 5th and holding about 1900-2000 rpm. Obviously with the gas engine you will be turning higher RPM than that, but the same principle applies. Lugging it with a load uses more fuel than spinning it up a bit and letting the engine not work as hard. Just experiment with it and see what is the sweet spot for your truck.
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Old 05-27-2020, 02:29 PM   #14
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I would suggest reading the owners manual. I've also seen separate towing manuals, either paper or online.
When I tow, I put my old 6 speed Allison in tow/haul and D, and usually use cruise control.
I don't like the shift response when braking going downhill, so then I will put it in manual and use the +/- to shift manually.
After a few trips I'm sure you will get the hang of yours.
Im with NMWildcat, read the manuals. There is probably a supplement for the transmission too, telling you how to tow.

I think we have already dispensed as to whether or not the transmission is an Allison 1000 or not so I won't belabor that fact.

What I can say is that when towing heavy in the mountains you need to drop your speed and drop gears to keep the RPMs up. This actually will have the wonderful effect of lowering the engine coolant temps as well as the Xmsn fluid temps.

I know this seems counter-intuitive to increase RPM to decrease heat but it works tat way because the engine is not actually working near as hard in that situation.
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Old 05-28-2020, 01:03 PM   #15
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same here turn on the tow/ haul mode put it in drive set the CC and go camper is 16,000 and when pulling my dump trailer with 12,000 i do the sam
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Old 05-29-2020, 07:37 PM   #16
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When looking at trucks, was told 6 speed was Allison and the 10 speed was GM/Ford get together. On my old 03 with the 4 speed, left it D and didn't use tow mode. If under 60 mph and it would down shift a lot. Then put in 3 and let it run. It had the 4.10 gears. My manual don't really say anything but use tow/haul mode. And it lists a 8 speed too. But not heard anything about it. Well will find out Sunday. Going to take the camper to the campgrounds.
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Old 05-30-2020, 05:09 AM   #17
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When looking at trucks, was told 6 speed was Allison and the 10 speed was GM/Ford get together. On my old 03 with the 4 speed, left it D and didn't use tow mode. If under 60 mph and it would down shift a lot. Then put in 3 and let it run. It had the 4.10 gears. My manual don't really say anything but use tow/haul mode. And it lists a 8 speed too. But not heard anything about it. Well will find out Sunday. Going to take the camper to the campgrounds.


I prefer to use manual mode and limit the maximum gear to what I choose by selecting that gear with the rocker switch. This will allow the transmission to perform normally but will only use any gear up to what I selected. For the highway, that means I have it selected to a max of 5th gear (my truck will not pull my camper in 6th) If I'm in a stoplight district or slow curvy, hilly terrain I will select a different maximum gear. If I want to use the motor to slow the truck on grades, I prefer to make the decision instead of the truck. -I'm a little odd. My car is a stick and I take a motorcycle everyday rain or shine as long as there isn't ice...I like being engaged while driving...control.

That being said...much has changed since the early days of 'tow haul'. You will not hurt anything by using or not using tow haul. It is a tool and is most helpful in interrupted traffic (stop lights) and hilly terrain for drivers who prefer less interaction in the driving process -read: put in gear and go. I've operated my truck like that and it performed fine but as smart as these transmission are today they cannot predict what the human eye can see in a changing road condition, they can only react to the present load.

The transmission in your truck is the tried and true 6L90, your motor however, is new and as a combo you will need to see what works for you.
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Old 05-31-2020, 01:13 AM   #18
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I use tow Haul mode in Drive for most of my trips. If I'm pulling a hill and it's dancing between gears, I'll drop it into Manual and set a highest gear limit like Big H describes. I have not had that happen on my 2020 2500 6.6 gasser yet but there is a hill that will make almost any truck do that with the right trailer behind it. Thats said, 5th gear and the 6.6 and the 3.73 seems to handle everything I've thrown at. Very happy with the combination of my trailer and truck so far.
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Old 05-31-2020, 08:20 AM   #19
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I don't know about the gassers and their torque curve or what works best for keeping them cool while pulling heavy.

What I do know is my 08 LMM 6.6 Duramax, Allison 1000 6 speed, 3.73 gears, gets it highest TQ between 1800-2400 with a Sweet Spot at 2100. I usually tow our camper at 62 (2000 rpm or so) because I get 10% better fuel mileage than I do at 65.

To keep from lugging the engine I put the xmsn in M5. This keeps my RPMs up, no lugging, and the engine/xmsn stay cooler as well.

When going uphill I adjust the CC and gears to keep the truck temps down, paying particular attention to the Engine Coolant Transmission Fluid and Exhaust gas temps. If the ECT or TFT are getting hot it needs more RPMS (drop a gear) to cool the if it is the EGT it needs less fuel (slow down).

Downhill I use the CC and Turbo Brake to keep the speed at the point I dont really ever need the brakes, I just let the truck do what it was designed to do.

For those with the older 5 speed Allison 1000s this works too, since the first 5 gears are identical ratios with the 6 speed. In fact you can add the 6th gear to an older 5 speed but the savings in fuel when not towing would never pay for the conversion.
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Old 05-31-2020, 09:09 AM   #20
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I don't know about the gassers and their torque curve or what works best for keeping them cool while pulling heavy.

...
The GM 6.0 gasser with a 9,500lb trailer and about 1000lbs of load in the truck you don't have to do anything to keep it cool. I drive the speed limit, stand on it if the grade requires while going up and use whatever gear is necessary going down to slow the truck/trailer. The motor temp never moves and the transmission temp on mine has never been above 185.
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