I have been having problems with my mpgs over the last couple months. I have a 5.4 and have only been gettting 10-11mpgs, which in my mind is terrible. I have an aftermarket dual exhaust, but that is it, and I also have noticed a lag in acceleration especially with hills. What should I try? Will a new fuel filter help? I currently have a 98 f150 with 135000 miles, and I replaced the air filter about 3000 miles ago. Thanks for any ideas and help!

 

Have you done other maintenance such as plugs, COPs, O2 sensors, fuel filter etc?