Spitting off the belts?

I found my problem to always be a junk autozone or advanced belt. Get a Gates belt. If that don't help check the pullies. You will usually find this happening when the belt bottoms out in the v of the pullyunder a hard pull. They will turn upside down the walk off..
Mine now stay on at over 8500 . stock 69 lower pully closer to crank and smaller diameter pully then a 70 and up style. A Hemi pully is the same with a deeper grove. Altenator is a GM race pully.

Fought my problem for awhile until I broke down and bought a good belt. I saw the recall at 9300 already and the belt stayed on. Once they turn around they are junk. They tear the cord on one side.

As I said if the belt sits on the bottom of the V take it back.