XTM MAMMOTH! Extremly fast! Best engine! Very easy to tune! Big truck. A piece of cake to work on. Not bashworthy out of the box. Needs a little bracing. I put a dadders cage and Barnburner arms and I have not broken anything. There is the diff. problem but longer screws and shims are the fix. I believe the Mammoth is more a truggy. And Jeff Guest did win the Colorado State Championship by 22 laps with the XTM Mammoth.