LilRoush

32.9 mpg on my trip from Minneapolis to Dallas a few days ago.
I see 30ish highway most of the time, and high 20s city.

04 Grand Prix GT

is yours a six cylinder?

LilRoush

Yes, a built six banger.

FoxGT

I get around 25mpg highway as of right now. You can get higher; i've tuned one project car to about 31-32mpg highway but it was also completely stock other than the tune. Had no extra power after the tune, but fuel economy picked up.