the BEST thing you could do to that is put a stock motor or spec motor or whatever motor ya want in it (depending in you speed control) and put a 17 tooth pinion on it. i did that to a midnight pumpkin i had and OH MY GOD... what a difference. it'll also help keep the front end on the ground cause of the gear ratio but it'll raise top end. i really don't know if they make any upgrades for them or if they ever did. but give that a try.
Cory