There is two wires on the top of the trans. If for any reason those wires are disconnected it will not shift.... I had the same problem on my 1997 dodge 4x4..
My 1996 Dodge Ram 1500 4x4 Automatic Won't Shift Out Of 1st Gear?
Check the throttle pressure linkage on the drivers side of trans under vehicle it is more than likely rusted tight . It would be the top lever on trans and it should move freely,if not pop it off sand the pivot ball apply a little grease to ball and put it back together. The trans should shift properly.