Transmission Help

[TurningWrenches]

Hey everyone, I'm new to the I am in need of someone help. I just got my hand son a 96 1500 with long bed, short cab, 360 engine and the 46re automatic 4x4 transmission. I got it from one omymy friend's who is stumped on the issue. It started having the typical slipping issues, not going into overdrive, then it would need to be shifted manually.That is when he got a used transmission out of a 97 from a pick-a-part and installed it. After fiddling with it for a while, it got go. But 2 weeks later, it started doing the same thing as before. Now it sits with on reverse. Here's the kicker, pulled the trans pan and the fluid is clean. No burnt smell, nice red fluid, and no chunks or heavy metal deposits/shavings. The magnet has typical amount of build-up but not nearly as bad as some I have seen. So being fed with it, he sold it to me for a steal. I really think it is a simple issue with the wiring or a sensor that has been over looked. Any suggestions would be helpful.

 

[PCT]

May be stupid but pretty basic, but if you think it is sensor or computer type issue, unplug the battery for 30 min. With that truck, usually the truck has a bad tranny, just because its a second gen, you could always replaces the sensors and wires and see it helps