so I ran into this last week. my truck has only 2700mi on it. took it to our techs at my dealer and found out some good stuff.
There is a problem with the 4wd-auto mode on all of our trucks. Basically, don't ever park and turn your truck off with it still in 4wd-auto. leave it in 2wd or 4wd. I forgot what he said is the issue in there, but the problem is being reviewed by GM engineering and has been for a little while. There isn't a "fix" yet but ther should be one before spring i was told. I'll let you guys know if i hear anything.