05 fuel milage need improvement

[Redneck47441]

A buddy of mine with a f-250 ex cab 4x4 with 33's is only getting 10mpg all hwy. with 90,000 on the clock. Here a list of we've gotten so far new turbo covered under warr.,fuel filters, new egr, new oil and fuel additive every tank. Its not smoking white so I dont think its the injectors. We just cant figure out why only 10 mpgs whats some of other things we can look at whats some of the thing you guys have seen or heard that could be holding it back.

[DoubleDpsd]

right foot? winter blend diesel?

[Redneck47441]

mabey a little right foot and winter blend diese,l but he should be at 13-15 not 10 with all that considered Ive heard him complain about mileage since he bought it. I didnt know if any other 6.0's was having mpg trouble could give me advice.