that makes sense . i dont do a lot of highway driving and im a pretty mild driver i get 15 ish
what i dont get is why my old 300 6 1/2 ton beater which i probly never had tuned right ( which i wore out after 300,000 miles) that carried a 600 pound welder an a lot of tools got beter mpg than my computer controled fi motor with an 5 speed with od. and i dont even load it down.
it must be possible to get at least as good mpg or even beter
that is my quest

 

Your Motor is capable of 20 I have a 92 completly stock that has allways got 17 arond home and has got as good as 22 on the Interstate if I would hold it down to 65. My brother had a 95 that he said was doing about the same. Both trucks had 5 speed mine has a 300 rear end his has a 273. May I sudjest droping down to the 6 cyl. forum. Those guys can tell you alot about the 300 L6

 

I think this is being over-analyzed. Have you done an ignition tune up lately? Checked the timing? Air filter? Changed the trans and diff fluid? The engine was designed to run with a cat on it, and removing it won't help things at all. Try to eliminate parasitic driveline losses as well as rolling resistance first, then experiment.

 

I know this is an old subject but oh well. I have a 89 F250 4x4 with the 300/ZF5 combo, stock tires and 3.55 gears. After removing my firewood racks and driving to/from work using the interstate w/cc set @ 60mph my best mpg was 17. Town mileage is around 13 with a feather light foot.

 

First things first. How recent is all the servicing? If anything drive train wise is overdue, do it. Next, you don't really have the best combo for mileage. Yes the 300/ZF5 is good, but it being in a 4X4 3/4 ton truck really is the deal breaker. There is a lot more weight in the 4X4 drive train as well as the extra weight of the heavier F250 frame. Honestly, what your getting sound about right to me. I wouldn't expect higher unless you change to a diesel...