RE: radio glitching
First I would plug the battery directly into the receiver and test again -you might have a bad switch harness. Then I would run the antenna forward away from the rest of the radio and range check again to see if your installation is causing noise. Then I would range check with only 1 servo connected and see if that makes a difference. There could be a problem with an aileron extension or servo lead. My bet is the switch - since you still have plenty of voltage, but there is a loss somewhere before it gets to the receiver.