I had a 2011 ecoboost 4x4 with 3.55s. Mileage seemed to improve after a few thousand miles. Much of my highway travel is East to West. On long trips, it generally got 18 mph driving West and 21-22 mph going East at 70 mph. Above 70 and mileage dropped.
I really liked the truck but had it in the shop three times in about a month at right at 60k for fairly major issues. Traded for an identical 5.0. The 5.0 gets a little less highway mileage and a little better city so averages about the same. It has less power than the eco, but sounds faster.
