I've detailed my experience when the subject of 'mpg' has surfaced in the
past.   '91 Vanagon with stock tranny and 195-75-14 Kirklands gets 25-26 mpg
on the highway, at 65-70 mph.  Mpg doesn't seem to improve if I hold 55-60
mph.   On a 200 mile run that starts with a full tank I'll put in 7.8-8.0
gals. to refill.  I always fill until the first 'shut-off' and hang up the
nozzle.

It is powered by an '89 RV 1.8 Digifant 2 engine.  The engine 'mods' consist
of a tightened AFM spring (2 notches) and an 8� advance (one belt tooth) of
the valve timing.  It runs lean enough that I have an almost dark grey color
to the exhaust pipe.  The temp gauge needle sits on the left edge of the LED.

All seats but the driver's are removed, but I've built in a folding bed,
installed the left rear Westy wardrobe/shelf module, and always carry 800 lbs
of machinery, supplies, and equipment that I use in my business.

It is possible.

Dana