I'm seeing 15.2 mpg combined city/Hwy with some trailering (12' tandem axle 3000#) I haven't babied the throttle all that much since 500 miles.
My specs are 2011 6.7 SD CC LWB 4x4 SRD U-Lariat 3.55 Axle
I feel I could possibly squeeze out maybe another 1 MPG if I wanted to slow down on HWY and accellerated a little easier.
The 3.55 ratio has loads of torque and feel that anyone considering the 3.31 should drive both vehicles.
IMO, I think the 3.31 will serve alot of people well and still provide ample torque and accelleration while getting better MPG.

 

Do you have 20's or 18's?

 

With Michelin 20's at 60 psi and an ARE cab high camper shell.
Uniden 76 CB radio, windows 99.33333% up or down depending on how you look at life.

 

I've got 2200 miles on mine with about 1300 of those with a trailer hooked up. Everything I tow is 9,000 plus. Skid loader, Mini Hoe, Dump trailer with broken concrete or my gooseneck horse trailer. Most of my mileage with a trailer hooked up is in town mileage.

My display shows 12.6 mpg for my average. So I know dragging this equipment around is hard on mileage.

 

This pretty much my experience. I changed the factory Michellins to Toyo MT's and have 15.2 over the full 5,000 miles. Breaking it out I get 18-20 highway, 11-12 towing and 15 around town. I'm not doing as much towing as I'd like and am spending more time in school zones than I'd like. Soccer Dad-ish. Yo.

 

I'm up to 500 miles on mine. I'm averaging 15.2. F-250 3.55 on 20's

 

Hey Epic, I forget what axle ratio you're running?

I don't reset my avg mpg often, just kinda watch it daily. Yet to see 18-20 MPG?

 

I have the 3:55 gears in the rear end. The Toyos are larger than the factory tires so that effectively lowered the rear end gears further. I also towed a hard pull up and over a mountain pass when the truck reached 600 miles to help break-in the drive train. It definitely worked as I saw a decent jump in mileage. After a second good pull, I noticed another improvement but it's been pretty flat since then. Wondering if the change of oil to 5W-40 is going to change it any.