Im a little curious about the mpg with my 06 5.7 4x4. its a single cab truck. all stock. When i first bought the truck i was getting close to 20 highway. now days im lucky to get 14-15. i change the air filter with every oil change at 3-4000 miles. I did change the tires from stock to 285/70/r17. The plugs have about 4000 miles on them. I use 91 octane mostly from cheveron when I can. Just a little confused as to what the problem could be. Could the Tires make this much of a change?

 

tires prolly dont help. how many miles? try running some sea foam thru and see if you cant clean up some gunk and improve a MPG or two

 

Its coming up on 80,000...ive used a can of seafoam on the las t 2 fill-ups. Any ideas on how long that stuff takes to have an effect?

 

Has the speedo been recalibrated for the new tire size?? Your speedometer could be off by 3 or 4 miles which adds up fast when your calculating mpg's.I am assuming your stock's were 265's and not 20 inchers?

 

Agree Taller 285 from 265 = WiderTires = speedo off + MPG down, Perhaps then justification for an SC!

 

ha! ^^^good call. didnt even think of that. To the OP: heres the proper way to use Seafoam:http://video.google.com/videoplay?do...0865726229173#

 

glad to hear that cuz i just bought a sc waiting for it to get here.

 

Winter blend fuel also gets worse mileage than summer blend.