The solution is, probably, simple. Use 5 cell pack or a Duralite pack with a 5.1 volt regulator. Use heavy duty cables from the RX to EACH servo, do not Y-lead the two servos from one cable, cable length of each elevator servo cable is almost four feet. In addition the servos may be defective in that they are operating at too high gain and are overshooting the neutral, I had this exact problem with 8231s on my F15 stab. Horizon changed the servos and I upgraded the F15 servos to 8411s, problem disappeared. Finally, and I know some people including BV disagree , upgrade your stab. servos to 9411s they are more powerful and have metal gears, which make them virtually immune to gear stripping if bumped. Both of my BobCats are so equipped and are a delight to fly, having given not a moment's trouble, and I have complete confidence in the integrity of the control system.
David Gladwin