4l80e transmission overheating

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.

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Reviews of the car

If it overheats while driving more than 25 miles an hour, the thermostat is bad. If it overheats while stuck in traffic only, either the fan motor or the temperature sensor/switch that controls the fan to operate is bad. This temperature sensor/switch is installed on the radiator. It screws into a threaded hole.

first thing to do make sure that you can fix the cable first before you proceed to another problem .. it will hard to shift if there is problem with the cable .. but in this situation .. did you check the trans . oil good or bad oil...like smell burned oil.. and if you shift manually its fine .. it might be the problem came on with the manifold pressure switch on the valve body..

Could it be possible the coolant lines are reversed not allowing the trans fluid to reach the cooler? The pressure line from the trans pump can easily be identified by taking it loose and directing the fluid into a container.

Bad head gaskets

If your car is able to go 25-30 miles before overheating,I have seen where a loose bolt or tensioner could cause you to go a while before overheat.The oil pump works but if the belt is loose,it cannot keep up with the required flow and slowly overheats.If this is not your problem,let me know and I will figure something else out.Good luck! Greg

Seeing as it seems you do not have any overheating problem other than when you are towing I believe that you need to make sure that when towing you do not have the transmission in overdrive unless going downhill. This is the #1 reason for transmissions failure while towing. Trans overheat = engine overheat
Hope this helps.

1. Oil coming from the ext. vent means Overfill fluid transmission or valve body problem (need to open the transmission to overhaul it) but usually overfill.
2. Do you have any transmission faulty code
3. If you pull a trailer, heavy load there is a function in PCM (powertrain control Module) that raise the pressure to compensate the slip at clutch pressure and if you unhook the trailer and go on the highway before the PCM learn it, it will shift hard. What GM call the "shift adapt". You probably have a 4L80E for transmission or the 4L60E depends on the truck's options.
hope it helps.