2002 GMC 2500 HD 6.0 4x4 AC Belt breaks about once a week, have changed 3 belts and 3 idler tenisoner. Last tenisoner purchased from dealer. With AC on idler tenisoner jumps around real bad. With AC off tenisoner runs smooth. AC cooling is OK, do you think problem is with compressor?

Sounds like you have a belt alignment issue.

That tensioner pulley is very sloppy - they all are.

Check the alignment really carefully.

Hope this helps.