I have a 2012 F350 4x4 deisel with 3.55 gears. When I first got the truck I was getting around 20mpg. Now the best I can get is 16.6mpg on a 700 mile trip. And when driving back and forth to work I get right at 15mpg. 50 mile round trip, with 90% on the interstate at 75mph. I think the mpg should be higher. One of my buddies has the same truck with 4.10 gears. And he is getting right at 19 highway

 

When's the last time you changed your fuel filters, air filter?? Also, mpgs will go down when running winter fuel.

I used to get 19/20 when I was stock, always lower in the winter though

 

Truck only has 19k miles on it. Changed out Air and fuel filters at 12k miles. So the air an fuel filters only have 7k miles on them

 

Are you in a colder climate? I know winter and winter fuel hurts my mpg

 

Southern Oklahoma, right next to Texas. I use the fuel system conditioner an cleaner every other tank. I use the same stuff, an treatments. That my buddies do with with their trucks. I just don't know why they are getting a lot better gas milage than I am. When they have lower gears

 

I noticed recently that my MPG has dropped not that its cold here in NC.

 

Have your driving habits always been the same? The reason I ask this is, my best fuel mileage comes between 60 and 65 MPH with the truck unloaded. With my 7.3, I can get up to 23 if I keep it in that range. However, if I push it to 70/75, I will only get in the teens. If I am towing my fifth wheel, well, all bets are off.