Tell me it's something simple.
 

89 2.9 V6 4x4

Bought it just recently knowing it was going to take work, learning as I go. Truck was towed in and dropped off, don't know if it was on a dolly or a full trailer, which might be significant later in the post.

Truck doesn't move when I shift it into any gear (it's a manual 5 speed), even reverse. However, if I put it in 4 wheel low (didn't try any other 4 wheel setting), it'll move in first and reverse (didn't try any other gear, didn't want to move it far). My recollection says that if you tow a rear wheel drive vehicle on a dolly, you have to take out the driveshaft, right? Drive shaft is in, but it's not spinning in gear when it's in 2 wheel. I'll have to put it up on stands and have a friend shift it so I can see what it's doing. I know the transmission has issue, guy said it was slipping out of 4th. Is something not hooked up right here that it would move in 4wheel but not in 2wheel? I shift it in 2 wheel and it just sits like it's in neutral.

id check the rear diff...that might have an issue...does the rear driveshaft spin when you try to move

If it's not spinning it's tranny or clutch issue...not rear end.

whoops didnt see that part lol

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Since it moves in 4wd but not 2wd , it is obviously a problem in the rear differential.
A tranny or clutch problem and the truck will not move at all.

edit
I reread the OP.
It COULD be a problem with the tranny output shaft , but not very likely.

werent those old ranger tcases chain driven?