Well when I was running the whipple I switched to the 8 rib set up when I went from 13 psi to 16 psi because of belt slip. Paxton could be a different animal though. Do you see any evidence of belt dust now? I know with me what also helped was using the gates green belt, denoted by an HD at the end of the part#, which was alot stronger and resisted stretching, which made them last longer. The HD belt was easy to identify, because the entire belt is green.