It sounds like a servo problem for sure! more of, a stripped gear, and if the servo is still working for the most part, it would be the topmost gear aka, the gear that spins the least.. ive had this problem several times.. its as simple as taking the gear out and spining it a little bit so that when you give it full cycilic forward or reverse, the stripped part, or the part missing some teeth, will stay in the back outta the way.. i have serval 450's that if you opened them up, there missing a couple teeth on the back of their gear :P