As it's been previously stated, it's the nature of the beast. You're driving a heavy, V10, block of a truck. All the mods together might get you 2 more mpg. But your mpg results sound like they are pretty typical.

 

It is pretty hard to beat the laws of physics. Energy (HP) required to move a vehicle (be it a bicycle or 18 wheeler) is proportional to the square of the velocity. The only way to work around that fact is to improve the prime mover's efficiency at increased HP. As stated, just slow it down and back off the HP, steady freddy wins the fuel economy race..

 

 

I have your exact same year/engine/2wd and 3.73
I have a bbk 65mm TB, Doug Thorley long tubes, 3" piping, Flomaster, 5 Star 91 performance tune and I get around 16 to the gallon and I don't drive slow at all.

 

I am getting about 15+ so far with a 2001 F250 CC SB 4x4.. I do a lot of hypermiling with Honda Insights, so I use what I have learned back to the truck. I have a Scangauge so I can see instantaneous MPG and trip MPG. Tires pumped up to sidewall cold PSI, 55 mph max, accelerate down hill and let off uphill (or at least maintain steady throttle down and up hill, let speed fall off), coast as much as possible, avoid hard braking. When accelerating, allow the tranny to shift at about 2k rpm and get into over drive before 45 mph. Find a slow semi and follow him at about 2 second to 3 seconds pace. I keep track of fuel mileage at ecomodder and fuelly for progress, make notes there.

You don't need fancy modifications to the truck. Keep the tailgate up, use lowest octane fuel. No need for pure-gas, E10 is fine. Takes practice (and a REAL driver) to get out of the racing red-light-to-red-light frame of mind, and into gas saving. Nascar's Carl Edwards hypermiled a Ford Fusion with Wayne Gerdes and set a world record... Ford Fusion MPG World Record

later

 

Me thinks "crummy gas mileage" is just part of the package. My 2002 F250 SD 6.8L with 141K on the odometer has recorded gas mileages ranging from 5.79 to 16.36 depending on driving conditions, time of year and fate!

 

In addition to the tonneau cover and slowing down that have already been mentioned I will throw in getting a harder compound highway tire along with sticking to stock tire size.

I live down south in San Diego and drive 65 mph on the freeway. On my 30 mile commute to work I might pass one person. I get about 14 mpg overall and my head isn't on a swivel looking for Johnny Law.

I dumped my stock sized 265/75-16 tires when the tread ran out and went to 285/75-16 all-terrain tires... -1 mpg overall.

If I drive 70 mph on the freeway instead of 65 mph... -1 mpg overall.

If I drive 75 mph on the freeway instead of 65 mph... -2 mpg overall.

I also have a fiberglass tonneau on the back.

In the end, though, it's still a 4 ton truck where aerodynamics were probably not in the engineer's top 5 things to consider when designing the Superduty.

 

Real MPG for a 6.7L... I am getting -> 11-12 city .... 17-18 hwy
No load other than say ~350 lbs in the cab (2 people, other stuff, etc) and truck bed (various stuff with a 26.5k Reese hitch (150 lbs). Total Cargo.. about 800 lbs

 

Possibly double fuel mileage performance by eliminating all of the junk hanging on the motor.
Also cut the purchase cost by thousands by doing the same.

I've heard 1960 cars got 30 mpg highway before all of the emission stuff was added. Nobody knows just how better cars and trucks would perform and save, save, save fuel.

 

That is the most ignorant thing I think I've read on this forum.

 

There are a lot of good suggestions here but you have to remember you are driving a 3-3.5 ton brick through the air at 75mph and that takes a lot of energy. The laws of physics don't lie. These trucks were designed to work not to be easy at the pump.

1. You could look into a Gear Vendors overdrive unit. But they are expensive and it would take quite a while to get a return on the investment. See here: Gear Vendors Under/Overdrive Ford Truck-Car-Van 2-Wheel Drive 4-Speed and 5-Speed Automatics.
2. Higher air pressure in the tires will help some.
3. 5star tuning on an economy tune could help.
4. Put a regular air filter back in. It has been discussed a lot on here that a high flow air filter is a fancy way of saying it does stop as much debris as a regular filter. Your gains here are negligible unless the engine RPMs are very very high.
5. Perhaps a nice set of headers and exhaust like a Banks kit could help with a tune. It will free up exhaust restriction.
6. Lowering the truck could help aerodynamics and reduce drag.
7. Buy a cheap beater car and use it for fuel economy. You could save a fortune on fuel and maintenance on your truck. Use the truck when you need a truck. You could get a relatively quick return on investment here.

 

Are your tires stock size? If not, your speedometer is likely off and giving erroneous readings for MPG. Mine had 34.8" tires on it from when it was new and the speedo wasn't recalibrated until it had 168K on it. I calculated the truck had actually more than 184k on it by that point, just from the difference in tire size. I then applied that 10% difference to the MPG and it was actually getting closer to 6 than 8 MPG.

I had a '99 F350 with the weak-*** 190HP (at the wheels) V10. Throttle bodies, headers, exhaust, tuners with custom dyno performance tunes.... Nothing made any difference other than a gear reduction. I jumped from 3.73 to 4.88 on 34.8" tires and jumped in MPG from 6 unloaded to 9. And even then, the truck didn't have enough power to tow anything over 8k. I was lucky enough to be able to purchase the KB supercharger when it came out and installed it along with PI heads from an RV engine. Even then, with proper tuning, it still failed. ridiculously.

 

Slow down, anticipate lights turning red and slow in advance, go easy on the gas pedal from a stop.
It isn't fun to drive that way though.

Sadly, you can save, save, save for 3/4 of a tank and then in one quick burst of speed to pass a truck undo all the savings.
My '99 F350 4wd got 16 mpg going on the highway at 65 mph 3 hrs each way. But 11 mph is my normal per tank around town, up and down the mountain driving.
My wife's '04 v8 4wd explorer gets about the same with our rural off pavement roads.

 

 

Staying under 2K RPM should make a noticeable improvement.

The problem is staying under 2K RPM until you get to cruising speed.