Loss of gas mileage-
 

Hoping someone can shed some light I have a 2010 Acura RL that has been a very good car. I have just lost 3 to 4 miles to the gallon. Recently have a new air filter oil, change, transmission and gearbox was flushed and refilled about 50,000 miles ago. This car has never had a tuneup. Change of spark plugs but runs fine also running premium fuel on it. Any ideas?