I thought I would post this, it's a random GM description of T/H mode May or may not cover all transmission's.
Tow/Haul mode significantly changes the transmission shift pattern to reduce shift cycling and to deliver better performance, control, and cooling when towing or hauling heavy loads. For instance:
Upshift points are raised at light to mid throttle position to use more of the available engine power for acceleration. Downshift points are raised to enhance engine braking to help slow the vehicle.
During deceleration, the torque converter clutch (TCC) remains applied at closed throttle at lower speeds to significantly improve the effect of engine braking.
During acceleration, the TCC is applied in 2nd range and remains applied in 3rd, 4th, 5th and 6th. This improves the drivetrain efficiency and significantly lowers transmission sump temperature when towing heavy loads. In Normal mode, the TCC generally applies only in higher ranges and is dependent on throttle position.
Tow/haul is designed to be most effective when the vehicle and trailer combined weight is at least 75 percent of the gross combined weight rating (GCWR) of the vehicle.
Operation of tow/haul in a lightly loaded or non-loaded vehicle will not cause damage. However, there is no benefit to the selection of tow/haul when the vehicle is unloaded. This situation will cause a firm shift. The tow/haul switch is not a performance switch.
Selection of tow/haul when unloaded may result in unpleasant engine and transmission driving characteristics and reduced fuel economy. Tow/haul is recommended only when pulling a heavy trailer or a large or heavy load.
Tow/Haul is selected or de-selected via a switch on the end of the transmission shift lever. A lamp on the instrument panel will illuminate to indicate that tow/haul has been selected.
Tow/Haul must be selected again, every time the vehicle is started, if desired.
2006 2500HD Duramax CCSB 2WD
2014 Crusader 285RET
Nights camped in 2013 - not enough!
Nights camped in 2014 37
Nights camped in 2015 40
Nights camped in 2016 35