The best I've ever gotten on a thankful in my '84 was almost 29 mpg.  This
was at an average speed of about 35 mph on moderately hilly terrain in
Oregon on a trip this summer, and I also have Daryl's (www.aatransaxle.com)
taller fourth gear modification.  Your best (reasonably safe) highway
mileage will be at 55 mph, hence the long forgotten (and I hope forever)
federally mandated speed limit.

Watch out for passing trucks!

Stuart MacMillan
'84 Westy w/2.1