MPG Help!!

I had some codes on my engine. So I replaced plugs, wires, cap, button, air filter, pcv valve, fuel filter, and I cleaned the egr valve and all of its components. It seems to run better but my gas mileage has decreased. It dropped somewhere around 8 mpg. I cleaned the throttle body and am waiting to see if that helps. Any ideas and thanks for the info. By the way, the codes are gone from the engine.