97 chevy 2500 pu Falling out of overdrive

chevrolet
2500

#1

i rebuilt a 4l80e transmission in a 97 chevy pickup.It shifts into overdrive then imediatly falls back to third.Anyone have an idea


#2

Possibly a bad TPS… I would start by scanning it to see whether the 4-3 downshift is being commanded by the computer.

transman