At risk of this getting messy and sidetracked quickly by wild claims based on 55mph downhill and downwind conditions, I am interested in some reasonable comparisons. Please lets limit to this to trucks with similar modifications knowing that they can be a significant factor and there are countless threads on stock truck mpg already.

Truck:

2013 FX4 Supercrew 6.5
3.73 gears
34.1" tires (Terra Grapplers @ 50psi)
Rancho QuickLift 2" leveling kit
Speedo set to 34.4 tire setting by the dealer (I presume the raptor setup, interesting reads about 2mph slow at 70 despite slightly smaller tires?)

I have now owned the truck for a few weeks and have been a little surprised at the mileage given what many people reported here. I got a little over 13mpg on my first tank with a maybe 30 miles of towing and a mix of highway / city leaning more toward highway driving (cruise at 70).

Tank two with no towing and a similar highway/city ratio and I am getting 14mpg. Tonight on the way home from work the 5min average hung around 13.5 +/- .3 for the full drive home with 3/4 of it being interstate driving at 70.

Does this check out for you guys who have similar setups? I would have expected around 15mpg with gears that should match the 34's pretty well and a heavy mix of highway driving with all of the guys reporting around 20mpg with stock trucks???

 

50 PSI in the tires...are they rated for that? I know some LT tires are, but P-metrics aren't.

Your fuel economy makes sense to me. The larger meats take more energy to roll, and the leveling kit really hurts your aerodynamics. My old truck, bone stock EB with 3.73s, would get 17-18 at 70 MPH. Throw in your mods and some city driving and I can easily see you down to 14-15.

 

Yep brido, I think ye're doing okay with that configuration. I wouldn't be disappointed, considering the way ye truck is modded up a bit, 3.73, etc. What I'd like to see ye report on is an all interstate trip of about 200-400 miles doing about 72. That's the way I drive, and to me, driving 72 or so on a long trip on interstate getting 18 or a bit more - hey, I'm good. I have never check around town driving, and of course my old truck doesn't have the mileage indicator. One less stressor for me, heheheheeee. When I get a newer truck with that feature, I think I'll turn it off except on road trips.

 

Brido. Some pics would be nice. I couldn't see what engine is in your rig. I get better mileage with my eco with 3.73 gearing, but I'm on stock tires and 18" rims. How is the performance on those big tires?

 

Considering that my 235's are 30" tires, you have some serious rubber on the road. Your MPG's don't shock me in the least.

 

The tires are rated for 80psi and with the weight of a F150 the charts say I should run about 40, but I went up a bit for summer conditions as they bulged a bit at 40psi.

The engine is at 3.5eco, are you suggesting include a picture of the engine to help further identify it?

Here are a few shots of the truck...

 

Great looking truck. I've also got the ecoboost so no need for a pic. You're moving some big rubber compared to my stock 18" wheels and P275 tires. Considering the size of those wheels I think your mileage is too bad.
Personally I love my ecoboost, especially when I hear that hemi just screaming trying to keep up when I push down on the pedal.

 

That thing looks nice!

 

I'm in a 13 kr super crew 6.5 ecoboost max tow package 3.73 rear end with 34" toyo at 2's. doing similar driving and getting 14-14.5, with the stock 32"s I was probably 16 or 17. I would do 65 almost the whole way on the 320 mile trip from where i live to where I was working on a construction project and get 18-19 on the stock tires so 20 is doable. My dealer claims they can't adjust my tires for any larger than the stock size so i haven't had my speedo recalculated. so i calculate it manually using this sites formula Bigger Tires and Gas Mileage: How to determine actual gas mileage?
for example i have a pic of my trip meter reading 14.0 mpg with 327.7 miles and 23.3 gallons of fuel used. after adjustment it says my truck is getting 14.89 mpg

 

These trucks do seem to be pretty sensitive to wheel/tire combos. you are rolling a lot more mass, plus that lift means you are pushing a bunch of extra air.
IMO, you are doing fine for the setup you've chosen.

 

If it makes you feel better, my new 2014 FX4 Eco with 3.55's and stock Pirelli's is averaging 14.3-60% highway and 40% back roads. I am on the third tank. First was 13.8, second was in the 14's and this tank (halfway through) is at 14.3. I am sure winter blend fuel is a factor and this is the most sensitive vehicle I have had with fuel mileage. The 5.0 I traded in was same configuration but with 3.73's and was at 15.5 the day I traded it.
We are driving big heavy trucks with over 300HP so they will not tend to get the best mileage. My 5.0 stayed in the 15-16 range daily but returned over 20 mpg on trips with mainly steady highway driving. I expect the eco would be similar.
You have a great looking truck BTW. Enjoy it.
For what's it worth, a buddy of mine has a 2011 GMC 1500 with the 5.3 and he averages mid 14's in his drive. Completely stock.

 

Did you get the TCM adjusted for the larger tires? It makes a big difference. Figuring the mods you have there. Your MPG is not a surprise.

I have a 13 F-150 Screw 4x4 with 5.0, 6 speed, 3.55 electronic lock rear axle, 7350#GVWR package. I downsized from 20" wheels to 18" wheels. I have been averaging +/- 17.5 mpg with 20 + on straight highway driving according to the on-board computer.

One of these days I will record miles driven and the gas purchased for a real test. I will record a GPS track to compare with the miles shown on the on-board computer.

 

Brido. I find my eco gets its best highway mileage with the tach sitting around 1900. Is your highway RPMs at 65 or 70mph lower with the bigger wheels. Maybe dropping a gear to get the RPMs up into the better of the torque curve might improve things. Just a thought.

 

If you're already corrected for mileage, your MPG matches what I got with my old 5.3 after mounting some LT275/65R20's on there (Goodyear Duratracs, but you have way more power on tap.

 

I have a 2013 EB short bed platinum. 3.73 with 285.60.20 goodyr wrangler duratracs. I have right at 47K miles on the truck, and 30 or so on the tires ( just starting to get noisy). general interstate driving or two lane with no stop and go. no 35mph winds. running 91 ethanol free, or 93 with ethanol. tuned with EDGE CTS for tires and level 1 tune im getting 18.5 avg. that is with me not going any faster than 60. going up to 75mph. I get right at 16-16.5 I run 1950 or so RPM at that speed. if you don't program for tire size it affects shifting, and all of the computer calculations are off.