I average 18 which is up from about 16 post intake, LT/HFcats, and CB exhaust. Lot's of hills where I live and I don't baby my baby. I could do better if I drove like grandma but If I wanted to do that then I'd turn in my mancard and drive a Prius.
I've done a few extended trips and if I keep her at 65 or below then she will hit 30+ MPG but I generally do the 10 over rule so I get about 26 MPG at 75. I run 87 octane. MO blends a bit of ethanol into their fuels too.