I'm pretty sure the motor will bounce off the rev limiter. Just like the MPH. If you hit 100 the rev limiter kicks in. When I was going over the Kirkwood Pass at 8000 ft I keep it at 55 and just kept an eye on the revs. Great sounding motor.:-X0A6

Unless you're custom tuned, then sky's the limit.}>

Man I want to know why my pickup is getting so bad mileage.. I bought it from the dealer a week ago and its a 2014 f350 super duty 6.2 with 3.73 gears and its got a flatbed on it right now. Driving pure highway 40 miles each way, I have been cruise controlling it at 60 to 65 and its averaging 10 to 11mpg, that being said I was also babying the pedal, slow off the starts and rolling when able.. How in the heck are you guys getting 15mpg!

Oh side note I took it into the dealer to have them check the pcm for an update and they said it's all up to date.

What tires and what size are on it? Whats your elevation and terrain? The flat bed also hurts fuel mileage. Cruise will cost you some mileage, how much depends on the terrain.

Should have mentioned pickup has 44k miles on it, but it's got 265/70/17 tires in pretty sure, it looks stock on the wheels bit to me, and we are at 300ft elevation with very mild rises in the hwy section I have been driving recently, like maybe 50ft vertical rises, we are currently looking for a regular box to replace the flatbed, but I wouldn't think that the bed would hurt the mileage that much.

Tires are Bridgestone duravis m700 265/70r17 just went out and checked.

With no bed sides or tailgate, the air does all kinds of crazy things on top of the bed and behind the cab, but what kills you is what goes under your bed. I just noticed you said f350. Is it dual rear wheels? If so, that's a lot of extra rolling resistance, and weight. I'm betting it's a heavy steel flat bed. The 350 is also siting higher in the rear and depending on spring package, the front as well. The higher it sits, the worse aerodynamics. Is it 2wd? Is your front air dam still on?

Not sure how heavy the flatbed is, it's a pretty basic bed with no extra boxes or fuel transfer tanks. The pickup is a single rear tire and its a 4x4, it sits pretty level actually.

I'm looking at getting a K&n filter for the stock box. Hopefully if we find a good box to put on the back the mpg would go up, just would surprise me it would effect it by 3 to 5 mpg..

I haven't lifted the rear end and calculated the gear ratio but the door tag says it's the 3.73

Your numbers do seem a bit low, I would be interested to see what a stock bed would yield. Jack up the rear and make sure a brake isn't dragging. You never said if the air dam is still on it. No check engine lights? Make sure your hubs aren't locked in the locked position. No alignment issues? What does your air filter look like now? My 250 ccsb 3.73 has seen a best of 17mpg hwy, but 15.5 or so is more common, and I have the same size tire as you. When my truck was brand new, my hwy mileage was about 12. I also didn't realize my hubs were in the lock position from the dealer for a few days.

And if it is a 350 that sits level, it has the heavy duty front springs, the bed is heavy, or someone has put a leveling kit on, which would make me wonder about the alignment. But some times with a flat bed and no wheel wells, it can be hard to tell how much rake the rearend has. Does this flat bed have a big headache rack that sticks up above the cab?

It's on the front air dam, I would have to check the hubs but I know at least one of them us in the standard auto mode.
Doesn't feel like there is a brake dragging it coasts quote well. Must better than my old 94 f250.

https://cimg9.ibsrv.net/gimg/www.for...06174df994.jpg

https://cimg7.ibsrv.net/gimg/www.for...01876bc5aa.jpg

As far as I can tell it doesn't have any alignment issues, it seems to track just fine down the highway.

Looks pretty normal to me. I don't see weight being much of a problem with what is pictured above. 60 to 65 MPH steady should be returning decent numbers, even with the aerodynamics of the flatbed.

If a brake is dragging, you'll see more brake dust on that wheel than the others, but the side pictured above looks clean.

I'd suggest that you check the speedometer/odometer against a GPS. My truck is way off from the factory (speedo reads about 4 MPH faster than the satellites clock me at), a number of people have mentioned that issue. Yours might be even further off. With 3.73 gears you should be less than 2,000 RPM at 65 MPH in 6th gear. (somebody with 3.73's correct me as I have 4.30's)

-Joe

So I did clock it with one of my speedo apps on my phone and it was reading off the bottom of the stick, and I didn't do it for an extended period of time but for about 4 miles I watched what it thought I had gone and what the odometer said I had gone and they were dead on together.

In 6th gear at 65 I think im about 1800rpm I can double check tonight when I drive 40 miles down to my daughter.

I did try something on the way home from work, roughly 10 miles of hwy I locked out 6th gear and traffic was running 50mph, I reset my mpg gauge and it was reading 13mpg for that 10 mile stretch..

I'm just trying to figure out why I'm getting 10mpg dry and grandpa driving and you guys are hauling 7 to 10k and getting the same.. Lol something dont add up!

Is that 10 mpg after a reset on the meter driving interstate or was that the average when you got it? Have you tried hand calculating your mpg.