I have an 08 F-250 supercab 4x4 with the 6.4L It now has over 20K on it and
average MPG's are 14-15 thats used solely for buisness and is run in the Mountians of W. Mass and Vermont.
Empty at a 55 mph it gets better then 17, sightly less at 65-70 which is were I usually drive at high speeds...