03 F250 SHORT BED SUPERCAB 4X4, 6.0L PSD, 10k,5/03 build date, flashed in Nov., AUTO, 37X12.5-17 BFG's with 6 inch lift. Camper shell 4 inches over cab.
When I bought this truck, I knew I wanted to do these mods. and pull a trailer, so a diesel was the obvious choice. I can allso accept the fact these mods would have a negative impact on fuel mileage. In town, 10 mpg, freeway, maybe 15 mpg. But when I tow my toy hauler trailer at about 9 to 10k lbs. I get 7 mpg. . When I talked to a service rep, and he found out about the modifications, he basiclly said I was S.O.L.
I just put in a Banks Monster Exhaust. Don't know yet if it will help mpg. Butt-o-meter says a little more power, and it's too quiet for my taste.
Anyhow, factory gears are 3.73, need to change to 4.30 to compensate for tires. May go to 4.56 gears.
Do you guys think this will help mpg? Can I go to this large of a ring and pinion and tow to rated capacity????

 

Seems to me that you should be getting better gas mileage than that. My truck has a 6.0 and is a long bed crew cab 4x4 and I get 16 MPG 80% around town and 20% interstate. My truck is stock but I have pulled up to 6,000 lbs on the interstate and maintained 15 MPG I got 18 on a winter trip empty and hope to get 20 now that it is summer on my next long trip. I use Power Service centane additive and it seems to help some maybe try that in addition to you other ideas. Good luck!

 

Higher (numerically) gears will probably lower your mileage....
I also wonder about your fuelage rate !
First let me state, I do not wathc my driving style nor my mpg !!!
I want to get where I want to go and I did buy an 8K lb truck...
so fuelage is not high on my priority list...

I get about 16 around the DFW area and we KNOW that's traffic central....
last long trip with 4 adults and two large dogs and luggage hauler hanging off the back I got about 18 @ SPEED (faster when the wife wasn't hawk-eyeing me :-)

I do have the Diablo Predator which seemed to help to the tune of 2 mpg or so...
and helped the performance IMMENSELY !!!
also, I do run the tire pressure up about 55 to 60 lbs unloaded...

I would suggest you check your alignment to ensure your not pushing your tires in the wrong direction, verifying the air pressure, getting the diablo predator, and when you can, keep it under 2000 rpms... that will still get you to 70 mph...

your large tires tires, lift, and camper over the cab are not exactly gas saving features,
but I would not think it would affect it THAT much...

Good advice on the powerservice fuel additive, it will help the fuelage a bit if you want to factor in the extra cost...

 

I believe, and someone correct me if I am wrong, the diff numbers are really number of rotations of the driveshaft input to one of the axles. So a 3.73 is really 3.73:1, etc. So going to a 4.56:1 is going to lower your mileage.

 

SBV45 you are correct 3.73 gears = 3.73 revolutions of the drive shaft to 1 revolution of the tire,
I'm still experimenting with the diesels but with a gas engine a lower ger can actually help with the milage (sometimes not always) with a lower gear the engine does not have to work as hard there for it is not draghting as hard,
that is kind of a theory I'm working on anyway,

now back to the subject at hand, Hooker I also have an 03' supercab short bed, when it was stock with only 1200 miles on it I was getting an avg,hywy/city 16.5 mpg, then I lifted it 8" and 38" SSR's I also installed 4.56 gears and now it down to about 11-12mpg, so I'm not sure regearing is going to fix the problem, I would say go with the programmer and see if it helps, if you do decide to regear you'll appreciate the performance gain, my truck with 38" tires performs very close to when it did with stock tires,

 

I was thinking along the lines of Skipped link. When towing, the engine is having to work too hard, with the 3.73 gears. Lower gears (higher numrically) will give back the lost torque from the bigger tires. 4.30 gears would put the powerband back to "stock condition". Towing the trailer at 65 it would run in fourth gear at almost 2600 rpm. Not enough power to allow it to go into fith. Tires are at 55 psi and wearing well (alignment). Would love to put in a programer such as the Diablo or Banks 6 gun but worry about warranty issues. Do they leave a traceable code?

 

I personally don't think there is anything you can do for better milage except go back to stock height, rims, and tires. Higher gear will even further aggreivate your milage situation..

 

One of the things I have found out about tire diameter, speed, and torque by racing on the Bonneville salt flats is a statement that was told to me about 25 years ago. "It's easier to pull a gear than pull a tire. Even tho your formula for diameter/rear gear maybe equal: ie: 38"-4.30 ='s a 32"-3.73 (don't hold me to the numbers please) the resistance of the tire will will take more horsepower/torque to do the same thing with the smaller dia.. I know a lot of guys like to raise up their trucks for the "look" plus your use of it but something needs to pay for it. The higher you have it, the more wind resistance there is. Look at the crosssection of your truck. Park it next to a stock one and stand about 100" feet away in front and look at them. If you want mileage, lower it and put the 3.55's from a E-350 PSD van and raise the tire pressure to 75 lbs. Hey that's it. If you add the aftermarket "speed" hop up stuff you could probably put it the 3'55's anyway. I would like these PSD's to go down the road empty at about 1700 rpm @ 75mph. Good Luck