So he flight planned a trip of some 550 nm without a fuel stop. I don't
know diddly about Mooneys, but iirc, 550 nm is pushing it pretty hard in
most singles, yes?

Trainers, yes. IFR cruisers, no. A Mooney is generally good for a
little over 5 hours endurance at 75% power, and you can expect to make
140-150 kts. If you pull it back to 60-65% and lean it, you can get 6+
hours at 130+ kts. 550 nm is easily doable unless the headwinds are
vicious.

He said he had 49 gallons leaving ABQ, and flew about
5:20. 9.2 gph. Is that about right for a Mooney?

Depends what power setting he was running. Many people run their
Mooneys around 8 gph for endurance. That would make sense given the
length of the trip, since making an extra fuel stop would erase any
time savings from going faster.

Before we jump all over this guy and make snide comments about too much
air in the tanks, I seem to recall not too long ago we had a pilot run
out of gas - only it turned out later than when his carburetor was
rebuilt, most of the parts used were for the wrong model or out of
tolerance, and the fuel leaked away. The NTSB still called it pilot
error.

Michael