Towing trouble..

[Benny315]

Going to have to ask what's going on here, what do I do??
If I drive around empty (no trailer) everything is fine, and got about 300 miles on the transplant so far. Hook to an empty dump trailer drive about 8 miles and back it up then forward and slips throwing tcm p0762. If I clear the code and try again right after it slips and same code, but if I unhook and drive around then come back for trailer it will be fine for a short distance. Reverse works great, have tried tow haul button, manual mode and even drop to first with same effect.
Just wierd that it will pull the trailer loaded even for a short distance.
What do you guys think I should try??

 

[Benny315]

The first time it did it, it also threw codes p0827 and p0826. Since I thought I did not need to hook the tap shift up it was all good until towing. So I went and got the tap shift from the donor and steering column harness, hooked the purple to the purple needing added to the harness repining and from what I could read here the orange went to 12+ so I found keyed 12+ in the steering harness big connector and tapped into it.
I assume I got that right since I'm down to the single p0762 code.
Also the dash display only works when it wants and when it did come on this engine/tranny is showing 235,000 miles.
So maybe my tranny is needing rebuild??
Just wierd it will pull for short distance and daily driving to work there is no issue.
Any help would be great and I will try whatever you ask.

 

[LCAC_Man]

Have you had the pan off at all? sounds like low line pressure, maybe the filter seal failed or filter is damaged/dislodged? Are you 100% the level is good?

 

[Benny315]

Never had pan off no. I changed spin on filter at time of transplant, install the new tranny lines and yes check fluid level often. I filled the trailer, reset the code and drove about 8 miles back home in "tow haul" with no problem. Upon getting home, reverse and forward to get trailer into dump spot it did it again.
I can feel it engaged and starts to move then slips out, and when that happens when going to reverse it makes a shudder noise. I stop instantly reset code again and is fine again for a bit. It does not seem to matter if I let the truck cool down or leave it running, as long as I reset code it will go again. Unhook trailer and can drive around all day. Thanks