sounds like it could be two things,first check the clutch make sure its kicking and turning the spur gear,if thats happening it might be your diff,im not familair with the model but i would bet on that,good news if its the diff its only gonna cost 10$ bucks ta fix,bad news ya gotta tear in to the tranny but thats fun for me,pay attention to how tight the diff is when ya put it back together too tight burn out to looose wont move /and/or burn out,see ya!