I've never liked the push-button 4WD selection on these trucks -- too much other stuff to go wrong, as opposed to the old reliable shift lever. You can stave off the ultimate failure and big costs by routinely selecting in and out of 4WD -- that seems to help, but I think you'll need a bank loan if it ever requires actual mechanic's rebuild. (Maybe I'm wrong -- maybe GM has a reasonable fix and I, a non-mechanic, just don't know about it...)