2001 fuel consumption
 

Hey guys, first poster here. I just bought a 2001 A8L 4.2. The official spec for highway consumption from what I've seen on the net is about 25mpg, but after a few hundred highway miles (hovering around 70-75) I'm only getting about 20mpg. It has around 120k miles and I don't know anything about the history, so I'm wondering what to look at first and if there are any common causes of this. Should I change plugs, get a tune-up, probably should do both but I don't have piles of money to throw into it. Also wondering what kind of mileage others are getting. Of course I'm running it on premium only, and the car runs smooth as silk. Thanks for any advice.