Yanked it into 4x4 to back out of drive way it started to pop and bang like diff was slipping.Doe's it in forward and 4x4 low also.Had it in 4x4 this summer to get camper through muddy yard didn't notice any thing.Could the ram on front axel not be engauging all the way.??Dually in ohio snow storm pretty useless with no 4x4.

 

Might want to check u-joints, just had to replace one on front drive shaft, not sure what the newer trucks have, but there is a double one at the transfer case that was known to cause many issues, it had on mine 6 years ago and I found it easier and cheaper to buy a remanned shaft assembly.

 

Kinda sounds like what happened to a coworkers truck. he never had any trouble with his untill one day he put it in 4 WD and it started banging and not pulling. The fluid had drained out of the transfer case somehow. he said he had never seen a leak. Had to put a new gear in it. the chain was okay. He claimed this could be done without pulling the transfer case. I hope it is something more simple than this.