I'm glad you said this, because this is exactly what I am getting for mileage, 16.8 avg lifetime to be exact. I also run mostly highway and cruise at 80 mph. But in my case, it's the first 1200 miles, so maybe it will improve now that its broken in a bit.My MPG have been pretty poor, ever since I got the car. I'm averaging 16-17mpg combined driving, and most of that is highway. Part of this maybe that when I'm on the highway, I'm usually doing about 75 to 80mph...okay, mostly 80mpg . But would that make such a huge deal on knocking down the MPG than if I was doing 70mph?