If it's intermittent problems, your gonna have to tear it all down and see whats goin on.. It's a pain, but lets ya learn about the models ins and outs.. I have to tear my Tornado down tonight some time.. The rear wheels quit pullin this afternoon, so I've got a diff or dogbone problem myself.. Im hopin the ears just sheared off the rear-main dogbone, but it was gettin dark and I couldnt see what was goin on.. Looks like it's that time of year for the drivetrain on these things..