I have had this issue for some time and am not driving the car. There is a clunk in the t case when driving. I replaced the chain in the case that seemed a little sloppy, then had the case rebuilt at a reputable shop. Swapped out the tccm still had the same prob. The motor on the case shifts fine but there is a clunk still when driving. It seems like the EMC will not stay engaged and that is what is causing it to shift in and out of 4wd. It also has new tires and new sensors and a clutch pak in the rebuilt case.