need help with steering problems

i got a gorilla maxx with g3 arms i have hi tec aggress0r crx . ihave a hitec hs-645mg servo . the problem is it turn right ok but left not so good. now i have made sure that every thing from the servo to the steering blocks is not to tight or rubbing. steering seems to be a bit slow. i am thinking of changing servos what would you recomend. or what do you think the problem is