I drove my '81 air-cooled, 7-passenger van to
Glenwood Springs and back (to Boulder.)

Filled in Silverthorne, then drove 263 miles,
over Vail Pass (10,500') twice and once up
throught the tunnel (11,000'+.)  Lowest elevation
at Boulder, 5450'.

Flat-out on I-70, 3rd, 4th gear, up to 75 mph.
All the time with the brick on the pedal.  ;-)

21.9 mpg, not to brag....

Richard