I had an '83 half ton short box 305 with low miles, and when I put a giant alternator on to accommodate my slow speed snow plowing, it would chew an expensive belt in no time, so I put on the El Cheapo $5 made in who knows where where land, and I never had a problem. Go figure.
I've had problems with expensive belts, and then no issues with cheap belts. I'd like to think that Gates is top of the line, but I don't recall if I had trouble with their belts to be honest. And I've got dozens of cars, including Corvairs, which are extremely hard on belts. Corvairs need a wrapped belt bcause of the 90 degree routing. It's the same style that are used in industrial machines. Wrapped belts have no exposed cords, so they can slip. On a Corvair, especially with a stick, you don't want grip, and you don't want to tightlet tensioned belt.
Getting back on topic, make sure your pulleys are clean with no rust and no burrs. If you have serpentine belts, look deep in the grooves for debris, it gets jammed inside, and you have to use a wire brush to clean it out, sometimes even with the engine running. Good luck with not losing your hand