I just wanted to let you know the batteries got here and are all charged up. As others predicted, it didn't fix the problem at all, so the other batteries are probably just fine.

I disconnected the motor from the rest of the truck and it sounds like a knocking noise inside the motor when a certin load and/or rpm is reached. I even took the motor off the truck and held it in my hand and it does the same thing. I switched out radio systems and it had no effect. Since the motor was removed from the truck and gave the same result, I can only conclude that the problem is electronic or electromechanical. I'm ready to poor gas on the thing and forget about it.