I had this problem on my '02 Suburban. No matter what I did, new belts would start squeaking after a few miles. The problem was likely a slight pulley misalignment, but before trying to replace a bunch of crap and lining up the pulleys, I tried a Dayco belt with the M-shaped ribs and it quieted it down. Never had another problem for the next 30K that I owned the truck. Might be worth a try: