Hello,my truck is a 2004 f350 6 litre extended cab and everything is stock .Both of my freinds dodges are deisels and are both extended cabs also.One is stock and the other has just a perfomance chip.One is a good friend and the other is a brother in law and both tell me they get over 20 mpg in the city.One lives in the same town that I do so were driving in the same terrain.Just yesterday for example I reset my fuel/mileage guage to zreo then headed 20 mins into down which is pretty much all down hill the way there.The best my mpg said was 13 and b ye the time i got back home it was back to 12.4 avg miles per gal.I dont drive my truck nuts and put my put into it.After hearing what the dodges are getting and the way fuel prices are going crazy here i have to improve this fuel consumption quick or sell the truck.I am thinking of installing a superchip to see how much that will help.If you can think of any thing else please let me know.Just another example of just how bad it is , for 2 hours of city driving that cost me $35 fuel.
Is it a dually? If it is, what rear gearing do you have? If you are in traffic mostly, with lots of stop & go, signals, & stuff, a SRW F-350 CC w/ an auto trans and stock 265 tires aired to 65 PSI should see about mid 14's average. On the open highway at 70, the same truck should see about 17. That's high "normal" for a 6.0 w/ an auto trans F-350 3.73 rear.
If you really gotta mod the truck, SCT makes a good programmer, and there are a couple of guys here that have some decent tunes for it. Just remember, though, a programmer is a performance mod, and its designed to use more fuel, not less. It burns it more effeciently, so if you're careful with your foot you might pick up a solid one m/g to 1 1/2 m/g for the cost of about $300. If you get a tuner, you need gauges to go with it, otherwise you stand a good chance of toasting the engine, and it may cause puking/head gasket problems. Your call.
You may be having more problems with your truck than a programmer can fix though. Have you checked the brakes? Aired the tires to max inflation (& are they in good shape)? Have you checked your air filter? How about the fuel filter? Do you have good fuel with no water in it? How's the EGR valve? Any boost problems??
Before you stick a chip/tuner on it, check everything else first. Make sure its in good mechanical shape, and then if you gotta mod, get the gauges to make sure you're getting the performance and protection you need.
Oh yeah - don't rely on the overhead. It usually reads a bit higher than if you compute it yourself. Always compute full tank refills, and fill to where you can see fuel in the filler neck. That's the ONLY way to accurately track your economy.