I would also check out that receiver pack very carefully. I had an experience with a 5 cell pack that wasn't assembled correctly. When you touched the pack, it would go from 4.8 to 6 volts and the servos would twitch. If you have one, connect your pack to a multimeter and move it around (the pack that is), looking for any voltage variations. In my case one of the bus bars hadn't been welded to an individual cell, the only thing holding it to the battery was the shrink wrap.

Andy