GTN 750 Course Intercept

I have a GTN 750 which couples to a S-Tec System 55X Autopilot. I am trying to resolve two issues when coupled the the A/P.

  • When capturing a course, for example a localizer following radar vectors, the tendency is to fly through the selected course before completing the turn, and then continuing the turn to regain the course, it seems the rate of turn is insufficient to prevent this, even on relatively shallow angles of intercept.
  • When switching from Heading Mode to NAV mode the aircraft initially commences a rather abrupt turn in the opposite direction to that required to intercept the Nav course, and then almost immediately starts a turn in the correct direction.

Any help with this would be greatly appreciated.