If not that:
check bearings in chaincase and skid
check secondary to make sure its not wound too tight
check brake is not hanging up
check primary spring and ensure its not broken or worn out, leading to slippage at engagement and belt heat and excessive wear
On top of what Modman says, make sure you have some cool air going in there. The REV traps in heat something terrible and if you don't have them, your sled would benifit from some vent kits.