Damn! The Turbo Arrow flew this route perfectly from KMRY for over 3 hours all the way to the right base turn for KPSP (next waypoint after PSP), and then turned the wrong way! It did a small "S" turn- turning left and then right onto the heading shown in the screenshot below. I continued on AP for a few more minutes, but she just kept going in a straight line.
Here is the cockpit view with the a/c in the location shown on the Nav screen above. AP is on, and coupled to the GNS 530. GPS DTK is 078, TRK is 123 - both are incorrect!