My 99 Silverado Z71 had a new transfer case at about 150K miles. I used the auto feature all the time (winter in AK) I knew It was going because I could hear the chain slapping the case.
On the other hand, my wife's 03 Trailblazer has the same feature. It stays in auto all winter, currently has about 140K miles on it and the transfer case is as tight as it ever was.
