cat440

me and my brother went sleddin today. he bought an '07 rmk 600 155" and i took out my z440. we were goin good through the ditches and we got too an approach he went up first so i gunned it and followed his tracks..smoked a dam culvert. it must have cut my track cuz about a half hour after that my track almost ripped right in half.. then his sled started acting up youll be goin fine and the check engine light comes on and it wont go over about 5500 rpm..but then it will quit and work fine then it just does it again out of no where.... anyone know whats rong.. we rejetted, unplugged the knock sensor, put octane enhanser in it and cleaned the powervalves.. anyone have a clue whats wrong.. also how good of sleds are the 2001 rmk 700's.. im lookin for one and i wanna know what they are like before i hand over my cash!