From what rc pitstop told me, & I'm not trying to act like I know it all, they said that the belt drive makes the gearing a little taller & works great w/xb sized tires. Anytime you put taller tires on any vehicle it effectively raises the gearing & those mt meats are really tall & prolly like twice as tall as the xb's tires. So my take on it is that the tall mt tires & the taller gearing of the belt drive has made your gearing really tall & moved you out of your lower power band but your top end should be crazy if you have enough power to use it. Maybe an 8k (or higher) clutch spring will help. I'll let the guys that have these cars chime in on that. I'm just going off my mechanical experience on trucks & atv's.