I have a 2000 2.5RS, auto, has about 46k miles on it. I think the MPG is about 21/27, but it seems as if I dont get that amount. Most of my driving is on the highway and I'm only getting about 20 MPG. I'm using 89 octane gas if that really makes a difference. I haven't had anything changed or replaced yet. Is there something that I can do to make it run more efficiently? Thanks.