I think there are a lot of factors that affect MPG, and those that are reporting mileage that good are driving under the ideal conditions. Terrain, traffic, altitude, octane of the fuel, etc. can cause your mileage to go down.
I've been using 92 octane most of the time, and have been driving back and forth between the St. Louis airport & Festus. I follow dip****s who cause me to break stride all the time up and down hills, and I get frustrated, have to pass in the right lane, and such. Plus, I don't baby this thing. I do about like Groucho, and need to have at least a good 100 MPH run every day. The rest of the time, I'm cruising about 50% of the time at 85-90, and the rest doing 70 thanks to the "left laners".
Having said that, I can STILL do all those, and drive for mileage...I just try to be smart about when I do what...and try to not ever use the brakes. I also do NOT leave it in 6th and dog the engine at all.
After break-in, my mileage dropped to just above 15, but I was also doing a lot of driving around town "Hey, look at my car!", but now, I drive mostly highway, and I'm up to over 19 average.
It sounds like you're right there with me, and I don't consider it abnormal. I only get 25 out of my 3.8 Bonnie driving similar, so I'm happy...and it runs well.
I do think it is funny that someone with the handle "enjracing" started a thread complaining about mileage
Gerry