If you got it to overheat not moving in the driveway, then you just ruled out the 4x4 system being part of the equation in my mind. Burp the system, make sure you don't have any obvious obstructions on/around the radiator, and see what happens.

If you're still getting the overheat after the burping, I think you're going to have to look at either a bad radiator or a bad fan clutch.

James