I just got a 2006 XLT Crewcab 4X4 with the 5.4L V8 about 2 weeks ago. I'm very pleased with my milage on 2 lane highways going 55 or 60mph, but when I get on the interstate and set my cruise on 70mph my milage seems to plummit. It seems like I get 18mpg or so going under 65mph, but only about 14mpg going 70mph on ther interstate. My truck is completely stock right now. Is this normal? Is there anything that can increase my interstate milage? I'm probably going to do the Gotts air intake mod pretty soon

 

That's normal. Your truck has about the same aerodynamics as a barn door.

 

So it's just the difference wind resistance between 60 and 70 mph that's killing it so fast?

 

It could also be the fuel/air map at the different RPM and load.

 

Same is true with mine. At 55-60... high teens, sometimes even scratching at 20. 65-70...15-16 or so at best. "Windage and elevation, Mrs. Langdon, windage and elevation."

 

I just got 17.6 on my last highway trip 05 fx4 supercrew stock

 

Enjoy it when your seeing 18mpg in a 4x4 with a 5.4L..... Some v6's average that and less. I havent checked my average for a while now but at one time was seeing 12-14 average. Combined highway and city. I don't monitor what I get on the highway vs city, as I drive both equally. I just average what I get per tank.

 

Feel lucky to have that MPG.
Took my 2007 Lariat Crew 4x4 to New York and back and averaged 15.6.

 

hey I just looked at your signature...was your truck the one in the offroad mags i read? i remember faintly a 2 door f150 with the fc/2's on it and there was a picture of the truck that looks exactly like the one in your sig, just wondering