I have a 1999 Lexus RX300 that should get at least 18 city and 22 highway, but I'm only getting an average 11.6 in city. I am a very cautious driver and never take off hard or run it aggressively. I have been using ethanol free gas and even a little fuel injection cleaner. It has 116,000 miles on it. Is there something specific I should look into replacing?!