1995 Chevy Truck Premature upshifts, no throttle response

Truck is a one owner, given to a grandson upon the owners passing. Has 5.7l, 4l60e, and manual transfer case. Transmission rebuilt. Have done regular tune up, including fuel filter. No check engine light. No broken wires. Tried unplugging ABS fuse, and checked temp switch as advised. Seems no one else has a clue. Not taking to an $80/hr garage for diagnosis unless absolutely necessary. Anyway, this is an intermittent problem. Premature upshifts (will go into OD at 20mph), no throttle response at 55+ (acceleration, downshifting, nothing), cycles from OD to 3rd on it's own. Torque converter is locking up as it should though. As soon as you pull it into 4WD, it runs perfectly. No problems except the front actuator doesn't engage and the 4WD indicator light isn't on. To put it into 4WD, you have to stop, turn it off, put it in 4WD and restart it. Again, only when it's acting up. If it's acting up and you just turn the key on(not started) the actuator does nothing or it cycles in and out. Actuator is new. Any thoughts? I don't want to go on a replacing 'skeet shoot' on this thing. There has to be a common denominator in there somewhere between two and four wheel.