jack up the rear of the sled and make sure the track moves freely to eliminate anything binding and holding the sled back. If all is good then Watch the primary as you give it throttle and and see at what RPM the sheeve tries to pinch on the belt. If you do find the clutch is the problem and it is not moving until 7500 rpm's, it most likely is a weight hanging up on a roller. The rollers could be rusted and stuck or a bushing on one of the weights is damaged and the weight is not straight and binding on the roller. If it is the clutch it is often cheaper to pickkup a used clutch on line cheaper than rebuilding. The rollers, spacers, and bushings on the spider alone can run $100- $150 not counting labor.