I got a 93 2wd automatic it shift 1st through 3rd fine and some times doesnt want to shift into 4th or overdrive then ounce it does shift it wants to randomly downshift some people said it could be a shift position sensor just hoping its not my tranny

 

This sounds similar to what mine was doing. I took off the tps on top of the pump and sprayed a little cleaner and lube and put it back on and it hasn't had a problem since.

 

Look at dnr customs for thier tps fix issue its a poteniometer dial thing wanna say it was like 30 bucks versus 200ish from dealer for a new tps....mine did that bs when I still had it rollin around on the road.....however I fried my trans in the truck....best of luck to ya