I run gatorbacks on all of my cars, they have been great - and quiet. I installed a 1 size shorter GB on my AC after throwing the stock belt and it hasn't come off since. And no issues with slippage on my supercharger. I highly recommend them. Like said above look for pulley issues. Something must be misaligned.
2008 G8 GT: Magnacharger TVS MP1900 @10psi, LS9 cam, 72# injectors,SLP Headers, Corsa catback