My '09 GT, 3 months old, 2.4 with 5 spd auto, air almost always on... In mixed suburban I've gotten anywhere from 21.5 to 25.5. One pure highway trip, air on, 65-70 mph, we got 28.5. When in a saving mood, I tend to watch the tach much more than the speedo, and try to get into 5th ASAP. Not always, ...