well i say terrible , its getting 10 miles to the gallon , i have a edge programmer on it set at the level two position. I had it on the level one , and it towed ok but just wanted a little more ummmph . No check engine lights or anything.
By the way this is unloaded not towing either. THe truck rarely gets driven , so its been going unnoticed.

Have you replace the fuel filter lately? Look to your air filter as well. And you might have some clogged injectors too because you don't drive it much...

F250 or F350 (or Van)?
Crew cab/extended cab/regular cab?
Dually or SRW?
Manual or Automatic?
4x2 or 4x4?
3.73 gears or 4.10 or other?
What size wheels?
What size tires?
Bug deflector?
Windshield visor?
Stock bumpers?
Camper/tonneau/cap/open/other?

Stock intake?
Stock exhaust?

Low sulfur diesel or Ulta-low sulfur diesel?

Believe it or not, ALL of the above can affect mileage. Your issue as stated is too ambiguous.

sorry , the truck is 2002 crew cab 4x4 .
fuel filter has been changed ,
Air filter has been changed.
stock bumpers ,
no wind deflectors of any kind.
not bed cover
35 inch tires on harley 20 inch wheels
How do i clean fuel injectors

stock intake
exhaust is a Magnaflow , downpipe , and resonator

Seems like I can get the bst mileage outta my durmax with 35 and 20's with my edge evo race set on level 7 long as I can keep my foot outta it.

How do i clean fuel injectors


This is what I use. A tad expensive but XPD is the second leading fuel lubricity additive on the market behind Biodiesel;

http://www.opti-lube.com/XPD.htm

Hi i have an 2001 7.3 its lifted 6 in and on 35's and the best injector cleaner that i have found is lucas fuel injector cleaner its cheep and u can get it any where at any parts store. the first time put half the bottle in then use it every time u get fuel. I picked up 2 miles per gallon with that. Do u have anything else donr to your truck?

I guess ill start with an additive. Thought about taking it to Ford to get a scan. But Ill try this first. Like mentioned , the only thing done is a edge programmer ,and Magnaflow downpipe and exhaust.

You should check this guy out at his website and on youtube. He may have your answers

http://powerstrokehelp.com/