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Old 07-08-2016, 08:13 PM   #1
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First time towing with Denali and have a few questions for the forum

I seemed to have towed fairly well I'd D but sometimes the Rpm's would climb up to 4K suddenly, I would drop to 3 gear and no luck , it wasn't until I hit the brake then it would drop. What would cause my rpm to spike from 2500 to 4000 in the blink of an eye??


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Old 07-08-2016, 08:27 PM   #2
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Transmission downshifting.

What style of Denali? Sierra, Yukon, Yukon XL, Acadia, Terrain?
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Old 07-08-2016, 11:12 PM   #3
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Quote:
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Transmission downshifting.

What style of Denali? Sierra, Yukon, Yukon XL, Acadia, Terrain?


Yukon , 6.0 v8 , just jumps from 2500 rpm to 4000 rpm Ina blink of an eye .


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Old 07-09-2016, 12:09 AM   #4
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Yukon , 6.0 v8 , just jumps from 2500 rpm to 4000 rpm Ina blink of an eye .


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What year?
Do you actually notice an increase feel of the rpms reving or do you only see it on the tac?

The mid 2000s GM instrument clusters have stepper motors that wear out. They can have iratic movement and then the needles quit moving eventually.
Hopefully it is this, otherwise you may have a trans or torque convert issue.
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Old 07-09-2016, 12:23 AM   #5
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Was this on flat land, hill or mountain? Did it feel like transmission was slipping or just working harder? How heavy is your trailer?
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Old 07-09-2016, 12:52 AM   #6
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It was going uphill and it seemed to need to switch gear so the cruise control just went nuts and went full throttle on the RPM's , it was loud and the cluster tac showed 4K.


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Old 07-09-2016, 01:07 AM   #7
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Don't use cruise control. The engine will run at higher rpms when going uphill. Do you have a tiw/haul mode button on your Denali? Putting that on while towing will help hold your fears longer before shifting. Depending on the hill grade you will want to downshift for going up and down a hill. Don't be afraid of higher rpms when towing on the hills.
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Old 07-09-2016, 01:18 AM   #8
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I was using the tow/haul button, so hitting 4K rpm is ok? What about when it seems to hold a high rpm for a while ? And it doesn't seem to switch gear? It feels like that is not normal, sometimes I will switch from D to 3 when I feel this. Sometimes this helps get that gear and sometimes it doesn't. Should I ever use 2??


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Old 07-09-2016, 02:06 AM   #9
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I was using the tow/haul button, so hitting 4K rpm is ok? What about when it seems to hold a high rpm for a while ? And it doesn't seem to switch gear? It feels like that is not normal, sometimes I will switch from D to 3 when I feel this. Sometimes this helps get that gear and sometimes it doesn't. Should I ever use 2??


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No need to switch to 3rd when its doing that. Its the torque converter working in its lock / lockout mode before dropping a gear.
I will have to look at my escalade tomorrow, but i think those motors are designed to handle 6,000 or so rpms.
If it makes you feel any better my big block boat turns over 4,000 rpms almost the whole time i run it. And many times i am running 4,500-5,000 rpms.
Granted marine engines are designed for that, while vehicle engines are more designed for fuel economy these days.

I dont think I've ever shifted down to 2nd gear, or 3rd even except on the older trucks, like my '88 or '96 chevys i had or an old powerstroke with the tow mode dropping off the OD.

Hearing you explain it, i think your fine. I bought a gas Silverado a month or so ago, and i am really surprised how much it shifts back and forth. My diesels hardly ever downshift.
My Silverado drops down, and revs to 3500-4000+ rpms, empty, not towing, running down the turnpike on rolling hills.
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Old 07-09-2016, 02:56 AM   #10
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The transmission shifting to a lower gear is what causes the rpm to go up. It is normal for the transmission to down shift when going up a hill while towing. If it stayed in the higher gear it would cause the engine to work harder. Lugging the egine is harder on the truck than 4000 rpm. Engines develop hp at higher rpm. Gas engines develop torgue at higher rpm than diesel.
Go ride a multi gear bicycle on hilly terrain. You will see that in the lower gears you have to pedal faster going up hill to maintain speed, but it takes much less effort than the higher gears. Same thing with you Yukon, rpm might be higher, but it is less strain on your engine.
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