I have a 02 F350 dually 7.3 Supertuner set on max. No mods. 19 city and with a two car hauler 48 feet at 75 mph, 16 mpg. I know everyone will yell at me. My 06 F350 dually 6.0 bone stock no tuner gets 11mpg in the city and loaded, same load gets no more then 12.5 mpg at 75 mph. HT

 

I have a completely stock 2000 F250 7.3L with 6-speed manual and 2WD. On a 2300 mile trip with open car trailer and about 7K pounds of extra weight I averaged 15 mpg at 70 mph. I get 19 mpg mixed city/highway all the time. Sometimes over 20 mpg. An exhaust and DP tuner would improve this significantly.