2007 Silverado 4WD not disengaging smoothly
 

I have a 2007 Chevy Silverado w/manual 4WD. Engages fine...works fine. When I go back to 2HI it takes 15-30 seconds to disengage. With a loud bang/clunk. Hasn't done this for the last 5 years now it started. Dealer changed lube in differentials and xfer case. Dealer rebuilt front differential and acuator. Dealer rebuilt xfer case and found a badly worn gear. Same problem exists. They have definitely tried to fix it but now they tell me this is "normal" and offered to show me it happens in a new 2012 truck. I wouldn't waste my time because I KNOW how my trucks have operated.
Any help on this??