The Trans will handle the 6s just fine. Got over 2 years on mine and gears are barely warped...
Go FLM Combo bulks and Hot Bodies hardend diff OR check this thread...
and go GA Bulks and LST2 Diff.
http://monster.traxxas.com/showthread.php?t=461995
OR
http://www.rc-monster.com/forum/show...f+maxx&page=15