Alright. I went to try the truck today, and the reverse worked. It works well when it's cold, but once the truck is warmed up, reverse fades away. Any clues?

 

Well, I would still like to know what's up, but I just bought a remanned tranny. The insides are COMPLETELY replaced, and comes with a new torque converter! That means any of the OEM design flaws are fixed. I think it was better than the local rebuild shop that wanted twice what the reman cost.