Same truck minus the 8ft bed here and I have averaged 12.2 overall according to trip meter B which has never been reset (16xxx miles).
I'm not a lead foot all the time but certainly don't baby it either. I've seen 15 on the highway and as little a 8 while towing the trailer.
2011 F250 6.2L XLT Crew Cab 4x4, 3.73.
Golden Bronze Clearcoat Metallic
2012 Coachmen Freedom Express 292BHDS
ARE Z Series Cap