Same for me with my 2007 charger rt, although I have a fresh air intake and 91 diablo tune, I run only premium and I have gotten as high as 30 mpg running at 60, up to Houghton MI as the speeds are only 55 on the 2 lane highways. can you use a diablo tuner on you car??? you could make some adjustments using that tuner, Diablo will do a custom tune for ya too,