This has been getting worse as time goes on back in late July I changed out the plugs and wires thinking I would get better gas mileage. Wrong. It has progressively gotten worse from like 320 miles to a tank to like 280 and now it flucuates from 220-260 since I got flowmaster mufflers installed. Any suggestions on what to do. It's really starting to get increasingly annoying considering gas is about to go up again.