Long time ASE mechanic here. On many chevy trucks I have seen people chase that problem replacing everything. In many cases a GM belt fixes it. They are made different, the grooves are deeper and the felt side surface is better. I have seen people replace every pulley/accessory, and the belt with a part store belt, and the only thing that would fix it was a GM belt. Bout 50 bucks.
***RIP Okie, GT will never be the same without you Mr Mayor!***