[suicideneil]

Do you have a nother motor to test, just in case? Im guessing not though. One more test you can do is to roll the truck back and forth by hand, with no motor/pinion in place, and turn the diffs whilst holding a wheel still etc, to see if there is any grinding occuring. The Neu motor will be a big improvement though, a worth while investment- your MM works okay on 5s you said... must be an older model = lucky devil.