99-7.3

[kp123]

i have a 99 7.3 f-350 ext. cab shortwb. i used to get anywhere from 18-22 mpg. recently i started getting 12-15 mpg. no matter how i drive it. so i purchased a programmer and an air intake hoping to improve ao little but it has no effect on anything. also the programmer shift very hard like give yuo whiplash hard in every setting except extreme. any ideas what would cause a rapid decrease in mpg, or how to fix teh hard shifting. thank you

[kainers]

my 02 always let me know when the fuel filter needed changing.She did this by giving me crappy fuel mileage.What is your maintenance schedule?

The hard shifting is the programming.IF you can take it back get a chip instead from a sponsor who can program what you want your truck to do.

[kp123]

well teh truck only has 82,000 miles and i change fuel filter pretty often. when i installed the intake teh turbo was all nasty from the stock intake with an oiled intake, dont know if that would make a difference, also i heard something about a loss of boost pressure will cause a decrease in mpg.