with 265's on mine with 139000..before the programmer or any mods,drove to Myrtle Beach with the family ,avg.21.2mpg. Roughly 70mph.keeping as close to 2000 rpms as possible..with some tricks,i would say its able to be done. BTW ..everyones engines wear and tear will make all the difference in the world.A pos engine will not get crap for mileage ,where as a tight engine ,would have to be better on mileage..just a thought.