Digital servos on 6 volts
I don't think it's a "high voltage problem", I think it's a voltage regulator problem, or your transmitter is being held too close to you reciever.
Did you try it without a voltage regulator switch? All of the newer digitals that I know of are designed to work at 6v. Putting in a voltage regulator will only reduce your servo toque & speed.
None, Nada, Zero of the last TOC pilots used voltage regulators, and they all ran 6 volts. (Nicads or Duralites) Try it you might like it. Don't be fooled by the switch manufactures advertisements.