They burnt up due to cheap batteries. I finally broke down and got a max amps battery and re-geared it as well. I have not had any problems with it burning them up since. I did not use the trans I made a custom one around the matrix tr center diff mount and the custom mount for that application available from RC-Monster.com (which holds the motor) I used the cent diff from the genesis tranny and a matrix tr 66t spur gear and the center diff lock. I used a piece of 2" 90 degree aluminum stock as well as a 2" flat piece of stock and some 1/4 steel brake line to mount the diff carriers to the chassis. My single speed seems like it hits around 50 mph or so, never clocked it so I am not positive on this.