Are you using alkaline-batteries (1,5 volt) or rechargeable batteries? If the latter on, the output from the holder is only 4,8 volt, which is not too great. And with alkalines they might not have enough juice to drive the servos to well either. Wait for the 5 cell pack and see if it gets better. I guess the servos draws so much power that there is nothing left for the receiver to receive the signals it wants to receive
