Check that the transfer case is engaging to do this jack all four tires up and lock it in 4x4 and look to see if the front is turing. and also make sure that the hubs work
I replaced the front driveline shift actuator and while I was under there I made sure the shift sleeve wasnt sticking....really easy $70 part and 30 mins sounds exactly like what I did...good luck
the 4x4 system on that jeep uses a vacuum line that engages it, check if the vacuum is plugged in properly or check if there is a vacuum leak some where on the front axle