possible believe it or not, has to do with complete setup and gearing and tire height and driving style.
I had a coupe with power heads (ported big valved e7's) with a big cam, edelbrock intake, 3.73, some lightening and a lot of suspension and I drove it from Lakeland to Lake wales for work (about 37 miles) all highway and got around 23 mpg babying it. (about 8 in town LOL)