I just did a full tune up on my 2.4 but my gas mileage hasn't returned completely yet. I just did a 500 mile round trip and only averaged 21.5mpg. I normally get 23 mpg with mixed driving. I recently changed my fuel filter and my air filter, is there anything else that could be affecting it? I did just go from 225/70's to 235/75's, but I don't think that is the problem since it really started before this.