I got 15 mpg, ONCE. Was on boy scout campout, and our convoy drove hundreds of mi @ 55mph. Van would prob still do 15 mpg @ 55, but "I Can't Drive 55!!"Just got back from a long trip after switching to 4.11 - San Diego to Crested Butte to Lake Powell and back. Best was 13.5, worst was 9.5 (trying to hold 85mph into a killer headwind on the 70). Mostly, I was just over 12. Fully loaded with gear and people.
For reference, the van got a record 15 mpg (once... usually 12-13) fully loaded, highway 75mph, before any mods.
2007 5.4L Extended E350 Wagon, ~5" lift, 33" Cooper ATPs, 4.11 D60, 92k mi