I've got the extended cab, 4x4, 5.5 bed, 5.4 with 3.55. My driving is mostly highway. I get between 15 and 16 per the dash.
2010 XLT Tuxedo Black Super Cab, 4x4, 5.4L, Westin Black Side Steps, Vortex Spray in bed liner, Firestone air compressor & rear air bags, Hornblaster four horn package
Towing: 2007 Grand Surveyor GS280, 31' travel trailer