when i first bought this car in 2006 i was getting between 305 and 320 miles per full tank (14 gallons). as time went on (especially within the last year) my gas mileage has strangely decreased to between 280 and 300 miles per tank (which in turn is costing me roughly an extra $6-8 everytime i fill up). since that has occured ive tried everything i could think of to improve my gas such as: replacing the air filter, ive replaced the spark plugs, bought brand new Yokohama tires (4), cleaned the junk out of my engine (twice) and not to mention ive been using certified synthetic oil since day one; yet still little to no improvement. also i "religiously" keep my rpm's under 3000 everytime i drive. with all this being said, have i done all that i can or is there something that i am missing that will help to improve my gas mileage?

if you really wanna dig into it, wheel bearings wear over time and can cause a drag while driving. thus more throttle needed. thus less mpg. also could be a dirty fuel filter.