Supercharger belt keeps striping!!

hey i recently supercharged (28psi) my 94 concord with the 3.3L engine and am getting 403 hp at the wheels, but the belts on the shupercharger keeps sliding. It lasts for like an hour before it breaks..like i know they slip a bit under high boost but come on! I keep getting different belts (supposibly the best ones on the market)and same thing! And its not the tension (i have at more than its suppose to be)
Any help would be great!!