How old/used are the servos?

Also check all the internal connections (servos to RX, extensions, etc.).

How old is the TX and when was the last time it was sent in for a check up?

Check the antennas on the RX. Make sue both ar OK (not frayed, kinked, possibly broken - you can also open it up and take a look to make sure neither one has come loose from the board.)

Set your failsafe to something besides "hold". On pattern planes I set mine to drop the throttle and bring everything else back to center. This is intended to allow you to know with a higher degree of certainty that you had a hold.

Aso recheck the receiver antenna geometry. Make sure that they are fairly close to 90 degrees at the end from each other and in a position that minimizes the potential for stuff to get in the way. I run straight back on the radio tray and the other one vertically inside the plane.

As far as power issues go, the Futaba radios has an intern battery failsafe on the RX that activates at 3.8 volts. You generally need to set it up. It is designed to drop the throttle to low and center the other stuff. Check confirm that this is the case. This is NOT the same thing as the actual failsafe, it is a separate feature. JR digital servos will generally stop moving at 3.0 volts, the RX will keep working down to about 2. volts. However that RX re-boots virtually instantaneously.

Hope that helps. We can talk more at the field.