I did a tune up.

 

With the taller tires your miles aren't accurate therefore your calculations for your mpg are wrong. Get a tuner and recalibrate your speedometer for the larger tires.

 

My 07 Supercrew 2wd with 145K gets 18mpg's on the Gryphon display but usually comes out closer to 17 hand calculated. 90% highway driving for me though.

 

Mine is screw lariat 2wd at 140k I got up to 11.2 today.

 

In the last year I did new plugs, COP's, O2 sensors, fuel filter, air filter, throttle body cleaning, MAF cleaning, etc and run a Gryphon tuner. I drive 20 miles one way to work with about 3 stops at the very start of my commute and average 60 mph.

 

04 Screw getting 13.5 on 275's on stock 18's. 80-100 miles a day. Varied but 80% highway/country roads.

 

Would definitely look into speedo recal. 5.4 screw with 6.5' bed, 4x4. Slightly larger than stock tires. I get any where from 14.5 to high 15's

 

I drive 300 or 400 miles a week in the country and get around 19 to 20. This is with my tuner set on trans mode which gives it a better shift. When I turn the tuner up I get around 22 or 23 MPG. My tuner and CAI helped me out a bunch. I can pull my skid steer or load the family up and go places and change what I need out of my truck by pushing a few buttons. Plus I can see all my temps and stuff on my screen of my tuner.