For what it's worth, I think driving habits have more effect on MPG than any other variable. Forgive the rambling, but a little zen can add a lot of MPG and and life to your vehicle.
I usually reset the odometer in my RL every 5,000 miles or so and it usually shows 18.5-19.5 MPG on average. I have a 14-mile round trip commute to work through town and usually drive at 8-10 MPH over the posted speed limit on the highway. If I'm behind the wheel, it's because I need to be somewhere else, so I like to make good time. But, compared to most others I know, I tend to drive smoother, anticipate traffic much further down the road and coast rather than keep my foot in it longer and then brake. Just to be clear, I don't drive line like an old lady either, on average, I probably stand on it a few times each tankful, either to get up to speed to merge, pass a car or just for fun.
Each morning I pull out from my neighborhood onto a 2-lane highway and traffic heading into town is usually heavy, especially if I've hit the snooze button a few too many times. Thankfully, I can see traffic for over a mile. When that little voice in my head says "stomp it and whip into that gap between the cars" that's approaching I think yea, I could do that, but why abuse my semi-cold engine like that, another, bigger gap always comes up and I'm honestly not in that big a hurry to get to work.
Another thing I do that it seems to me that most folks don't seem to do is carefully watch traffic on overpasses. If I'm in the right lane on a highway and I see a car on the overpass turn onto the entrance ramp, I immediately scoot over to the left lane, anticipating that they will come down the ramp at the same time I pass the ramp. As a result, I never have to disengage my cruise control and scoot peacefully by as the clueless driver(s) still in the right lane and the person on the ramp take turns hitting the brakes and jockeying for position.
Keeping your traffic radar on high, and chilling out adds MPGs, makes your car last longer and is a much more peaceful driving experience.
PS The left lane is for passing, you won't ever catch me in the left lane unless I'm passing someone.
