Hello Ed,
When you have a G3X Touch system with a GAD 27 and autopilot servos, the GAD 27 performs the function of pilot/copilot trim switch mixing, and drives the trim inputs on the servos, but it is the servos themselves that drive the optional trim motors. You do not need a third party device to perform trim motor speed control.
Speed scheduling of the trim motor drive signals to run them slower at high airspeeds and faster at low airspeeds (e.g. in the pattern) is provided by the servos both when the autopilot is engaged and disengaged.
Let us know if you have additional questions.
Thanks,
Steve