[Shotimes] gas mileage issues

[Hartberger, Jason M. ATAN]

I found out on my way back from Pittsburgh that my SHO will go precisely
421.6 miles before the engine dies. Fortunately, I found this out as I was
coasting into a gas station, so no harm done, but it raised some questions.
At that gas station, I put 17.6 gallons in my tank. Having done the math,
that averages out to 24mpg. That seems a bit low to me... is there anything
wrong with this number? this is going all highway, so I thought I'd be
getting closer to 30mpg. Am I just delusional, or do I need to have a
look-see at my engine?

Any help would be appreciated.

ATAN Hartberger, USN
USS Theodore Roosevelt CVN-71

94 red ATX, 19320 miles -- it's hexed, I swear (get it? huh?)