I drive a 2015 4x4 double cab with the 4.3 and have racked up 36,000 miles so far. It spends about 60% of its time between 70-75 MPH, 30% in city traffic, and 10% on sandy, rutted logging roads. The computer says it averages 20-21 MPG, but my calculator at the gas pump is very consistently 18...