I've searched the archives but couldn't find anything specific to my problem. Was wheeling last weekend in 4HI. When done, I backed up 10' to unlock the hubs as usual (auto hubs). Seemed to unlock fine. Drove on highway for about 15 mins. at 65+ mph with no problems. Turned off ignition. Started truck 10 mins. later and began driving. As soon as I started accelerating, I had a consistent and hard "clunk, clunk, clunk" as the wheels turned. It felt and sounded as though it was coming from the rear. Stopped immediately, put it back in 4HI, went forward about 20 ft. (hubs locked up fine), took it out of 4WD and backed up. Problem solved. Haven't had it in 4WD since last weekend. But every once in a while I'll still get that "clunk, clunk, clunk" although not quite as hard. It only happens when I first start accelerating. To me it sounds and feels like it's trying to lock itself into 4WD, but not engaging all the way. Then it disappears. So, I repacked the front wheel bearings a couple days ago, and I had to replace the wheel bearing adjusting nut on the passenger side (the little pin had broken off). Could it be that it's trying to engage the 4WD? What should I check next?