Sorry for chiming in late on this thread.  I've kept a mileage log since
purchasing my van in 1995 with 4,500 miles on it.  Now, with 123,000
miles on it my overall mileage--every drop of gas I've ever put in
it--is 16.9.  On the highway the best I can do now is 17.7-17.8 mpg at
3,200 rpms, about 58mph.  If I drive at 3,600 rpms mileage drops down to
16.6-17.3.  That's with an automatic tranny and Michelin 205/75 P14C XCA
tires.  When I bought the tires I thought the taller tire might give a
little better mileage but that doesn't seem to be the case.

Question:  wouldn't the best mileage be at or near the peak of the
torque curve?

Bob Trousdale
'90 Westy