I know futaba sends out their signal in packets....like channel 1, 2, 3 and 4, then 5, 6, 7, and 8. Whenever I group two servos together, I make sure to have them on lower channels. Like channel 1 and 2. Not sure if JR is the same or not. But this is one of the biggest reasons I left JR and went futaba. I fly helicopters and not matter what I did I could never get my swash to move level with my JR (9303).

Try using channels close together and see if that helps.