I have had 3 - 5.0 motors, 2013 STX Supercab 6.5 bed, 2014 XLT SuperCrew 6.5 bed, and now 2016 XLT Supercab 8 ft bed HDPP.
All 4x4, but first 2 had 3.55 gears. Both those trucks would easily get over 20 mpg on the highway empty up to 72 mph.. (best ever 24.5 Denver to Durango and back on one...