Scotty, I have a 1996 GMC Sierra 1500 with the 5.7L v8, and I have been having issues with the belt squeaking. It used to only do that if the belt had some sort of moisture on it (rain, dew, fog, etc.) It eventually got worse and squeaked all the time. When I looked under the hood, it looked like the tensioner pulley bearing went bad because it was wiggling back and forth just slightly. I replaced the tensioner with one from oreillys, and that didn't fix it. I then replaced the belt, but now it squeaks only at anything above idle.
well, either you got a cheap belt or tensioner, or one of the devices the belt drives has a problem, out of alignment or worn bearings