lost gas mileage

Tire pressure is critical to fuel economy. Be sure your tires are inflated as per the information in the owner's manual. There should also be an information placard on a door jamb. If you can't find the spec anywhere, try 35PSI cold for car type tires and 45 PSI for truck tires. After that. I'd check the air filter. If that's all good, consider changing fuel brands, lately the fuel companies have increased the ethanol percentage. I suspect that you're using fuel with a high ethanol percentage. The higher the ethanol percentage, the lower the mileage. You may try a different name brand for a while, and check the mileage. I tend to buy the cheapest fuel I can find and I can smell ethanol in the cheapest brands, has a telltaile smell kinda like garbage. Try Chevron, Shell, Union, whatever big name brand for a while. One more thing, I think new tires are al little more flexible and roll with less friction than old tires, using more fuel.