Just curious if anyone can give me an estimate on fuel economy on the chevy Avalanch with an 8.1 liter vortec engine that is driven (easy) without a trailer. (maby around 60 to 70 mph. Do you all think it will get better than 10 to 12 as which i currently get a 70 mph with my old 5.7 liter TBI chevy truck.

my father owns the 8.1 engine and he gets about 12 around the city and see up to 16 on the highway, its really not that bad for the size of the engine and 410 gears