I agree that there is nothing wrong with the Garmin 155XL GPS. Not as nice as the G430/530 or later, but still capable of doing the job.
Incidents like this, and Benalla, and even Lockhart R say something for my "belt and braces" practice of always having at least two GPSs operating in the aeroplane even if the other unit is a portable. Having spent many hours in front of a G430W in the panel and a G496 on the yoke, I can't recall them ever being in disagreement on my position for any length of time, although I have had one or the other drop out for a period.
As I recall, the Lockhart R aircraft was scheduled to have terrain warning installed and the Benella aircraft was to have an avionic upgrade including GPS. A Garmin 496 with the terrain warning turned on may have saved both.
Dr 