in my honest opinion, and i am speaking from experience. . .i would upgrade to a 2.4 Ghz Radio system (spektrum, futaba FAAST, ect) for the simple fact that you have no reason to be messing with crystals any more and since i have had mine i haven't had any interference issues like i used to have, and that may be part of your problem as far as that goes, interference is a big thing with R/C anymore because of all the remotes and what not in the area where ur running, like me for example when i was using crystals there was a guy that had a CB radio that would find the signal i was using and make me have a run away, thats how i broke my chassis the first time, with a 2.4 gig radio system you wouldn't have that problem, but as you said it may be a battery problem or as the other user said it may be a throttle return spring problem, i would address the cheaper problem before i go upgrading my radio.