I'm driving a 2014 silverado v8 4x4 averaging 19 and that's about half highway half city. With ALOT of stop and go traffic. On a straight highway run, I'll do 23 easy at 75mph. It's got ~5500 miles on it now and just had oil changed yesterday. I expect a slight increase in fuel economy.
Maybe you could hire on with one of the Big 3 because your mileage exceeds what the professional factory drivers get when they baby the vehicles for CAFE.