96 Z71 4x4 no power to rear wheels

Just bought this truck a couple weeks ago most of it seemed fine to the naked eye some cosmetic problems, door locks, muffler, and power steering pump, and some other minors. however i was doing some light 4x4 in our back lakes aria and thew truck shut off ue to over heating. let it cool down put some water and coolant in it and got it home. replaced radiator, top and bottom hoses, thermostat, and then found out the leak was the water pump. replaced and problem solved... however now when in drive reverse or any other gear that makes the vehicle move, it does not. maybe an inch or two. its almost like trying to drive with the e brake on. yes i have checked that, also changed tranny fluid and filter. I am at a loss and have put all the money i have into this and am missing out on work. is there anyone who can help me with this? again its a 96 Z71 silverado k1500 4x4 5.0 . is there a sensor that i missed. tried adjusting the shift cables and what not it wants to move but just wont do it.

need more information: If you put the truck in neutral will it roll? Trying to find out if the truck is stuck in place or is the tranny just not getting going. If the truck will roll in neutral I would look at the transfer case and the trans. If the truck doesn't roll, you will have to jack jack up either end of the truck and see which axle is not allowing it to move.

when you put it in gear and try to make it move, what is the engine rpm doing? does it labor trying to move? or does the rpm just run up?