Ford?s F-Series pickups have been America?s best-selling vehicles for years, and now they are becoming the most fuel-efficient pickups, too, thanks to a new engine lineup. An all-new 3.7-liter V-6 is projected to deliver best-in-class 23 mpg highway, pending EPA certification, plus the new 5.0-liter V-8 engine is projected to deliver best-in-class 21 mpg highway,…