Hi MooneySpace! I recently had dual Garmin G5s installed in my J along with a Garmin GTX-345 Transponder/ADS-B, w/o built-in GPS.  I had an existing GNS-430W which will remain in the panel for now.  I also have an existing STEC-30 AP with Alt Hold, which now uses the G5s for roll steer, and therein lies the problem.  My installer tells me that the Garmin STCs (I'm not sure which one(s), but I think it's for the G5) do not yet support the combination of G5-430W providing roll steer to the AP