97 Suburban Won't shift while towing

When towing uphill with my 97 Suburban 1500, I will get intermiitant instances when the transmission will not shift ??? The RPM's will bleed off until I'm crawling ~40 MPH. It does not matter what position the gear select is in.
When I don't pull the trailor tis never happens??
Engine has just been rebuilt, no codes.

When towing uphill with my 97 Suburban 1500, I will get intermiitant instances when the transmission will not shift ??? The RPM's will bleed off until I'm crawling ~40 MPH. It does not matter what position the gear select is in.
When I don't pull the trailor tis never happens??
Engine has just been rebuilt, no codes.
explain better whats happening. like at 70mph going up hill transmission will not down shift automaticly or manually to any other lower gear locked in high gear....if engine overheats this could cause loss of power no matter what gear trans. is in........

Similar to what your saying. Transmission seems to get locked in high gear and will not automatically or manually shift to a lower gear. Engine temp seems normal. Had a heavier duty torque converter and larger transmission cooler installed a few years ago.

First step is do have a trans capable scanner hooked up while the problem is happening to see what is going on.

//2000CAYukon

Similar to what your saying. Transmission seems to get locked in high gear and will not automatically or manually shift to a lower gear. Engine temp seems normal. Had a heavier duty torque converter and larger transmission cooler installed a few years ago.

i did a little checking about this shift lockup only when towing. it was brought to my attention back in 2000 that when towing do not put transmission in D4 keep in D3 this will protect transmission from overheating! not engine i guess there is an overtemp sensor in transmission and if it goes above 375f strange things can happen.

Will a suspect overtemp sensor trigger a code?