Can't figure this !!!!! I drove to Reno when my Suby had 500 miles on the odometer and got fantastic mileage. 33 going 34 returing. Evervbody else was reporting mileage in the 28 range. Just turned 3500 on the odometer and drove to BC last week..a 1000 miles R/T. Mileage dropped to a steady 28 the whole trip. On both trips the trip MPG reading was extremely accurate....reading the same MPG as I was calculating. Only thing different was during the first trip I never exceeded 60 mph. On the BC trip I was running 70-75. Does speed really have that kind of effect?