From what I am getting you have a GY240 on your T-rex right now. And you just added the 9650 futaba tail servo.............BAD IDEA
The GY240 is not compatable with digital servos. I would stongly recommend putting the GY401 on it immediatly before any further flights. So far that is a setup that is pretty much impossible to top at this point in the game. Untill a lighter "9650" comes out. If hitec would hurry on theirs......we would be all set