[Big Dave]

OK. Numbahs.

First tankful: 548.8 miles 19.293 gallons 28.44 MPG
Second tankful: 510.6 miles 18.272 gallons 27.91 MPG

Overall: 28.2 MPG

This is over my usual circuit (one-third each urban/suburban, two-lane state roads, Interstate). Flat terrain Hot & humid (low air density)

Urban/suburban - run along with traffic
Two lanes - 60 MPH = 1125 RPM
Interstate - 70 MPH = 1310 RPM

At all fillups I eye-droppered in the last drop she'd take.
My speedo is perfectly adjusted for relatively new 235-85x16E tires @ 100 psi

I baselined (no GV) at 26.4 MPG. Base MPG down because I cut down the air dam & removed the side skirts. Even I could not stand the things.

The difference in the tanks (about a half-MPG) may be an answer to the old question about windows down- no A/C vs windows up with A/C. First was run driver's side window down and very little A/C. Second tank was windows up and A/C on recirc.

On both tanks, I was on my hypermiling game.