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Tow haul mode has no change on transmission operation. Truck barely moves a 6000lb trailer when starting off on a hill. 3/4 ton with a 6.0 and 3.73 rear end.
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Tow/haul mode enables the operator to achieve enhanced shift performance when towing or hauling a load. When tow/haul mode is selected, the tow/haul switch input signal to the body control module (BCM) is momentarily toggled to zero volts. This signals the powertrain control module (PCM) to extend the length of time between upshifts and increase transmission line pressure. Cycling the tow/haul switch again disables tow/haul mode and returns the transmission to a normal shift pattern.
Would't trust it , take an have DTC'S - diagnostic trouble codes checked by a qualified repair shop with a factory or professional scan tool . Auto part stores can not check BCM code's .
DTC B2722
Tow/Haul Switch/Indicator Always On or Inoperative
Step
Action
Value(s)
Yes
No
1
Install a Scan Tool .
Turn ON the ignition, with the engine OFF.
Cycle the tow/haul switch while observing Tow/Haul Mode on the Scan Tool .
Does the Scan Tool display Active when the switch is first pressed, and then Inactive when the switch is pressed again?
--
Go to Intermittent Conditions in Engine Controls - 4.3 L or Intermittent Conditions in Engine Controls - 4.8 L, 5.3 L and 6.0 L
Go to Step 2
You need to have a diagnostic scan tool hooked up ,glitch in one of the control modules or a wire in the circuit shorting to ground ! probably something simple but hard to find ! With a factory scan tool they can check the input signal to the BCM ,PCM .
Tow/Haul mode enables the operator to achieve enhanced shift performance when towing or hauling a load. When tow/haul mode is selected, the tow/haul switch input signal to the body control module (BCM) is momentarily toggled to zero volts. This signals the powertrain control module (PCM) or transmission control module (TCM) to extend the length of time between upshifts and increase transmission line pressure. Cycling the tow/haul switch again, or cycling the ignition switch disables tow/haul mode and returns the transmission to a normal shift pattern.
Try turning on/off tow haul mode, it changes the gear ratio as soon as you turn it on/off to help with pull hills and such. If its not that check wires between there and tranny, if not that then you should probably rebuild the tranny.
If you think it could be the overdrive, try driving with the transmission selector in 3rd, rather than overdrive. If it helps, may have diagnose the problem.
Another option, not sure if that year model had the tow/haul function, where you could set the transmission shift point to change because you were hauling a trailer.
If you can narrow down the problem to the transmission for sure, I would still start with a transmission filter & fluid change, cheaper than rebuilding a transmission.
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