How are you guys calculating highway MPG by itself? I guess I should look at my owner's manual, I think my instrument cluster is calculating combined fuel economy for the overall miles.
16-17mpg sounds normal for combined on stock if you're using the throttle a lot. But I usually go 70 in 65 zones to avoid police entirely.. I'm thinking I might get better fuel economy at 75 and the sixers use mid grade fuel in their cars to gain a couple mpg without a tune I'm going to try that some day as well but gas prices are sky high right now.
Also you realize that summer blend fuel is different than winter time and that some gas is not as good as others. For example, don't use arco in these cars unless you don't like your car. I use chevron but I'm going to switch to conoco phillips (76) and try it because the last two fill ups of Chevron I'm not so sure about. I've always used 76 in my other car with no problems. But that car was getting me 29mpg