"We can just agree to disagree because even in the absolute best conditions with flat roads and no stop and go traffic I'm still having a very very hard time believing you... "
Since you have twice called me a liar, which I am not, there is more than mere disagreement here.  Just because you do not know how to drive efficiently or more likely simply choose not to does not mean that others cannot.  Frankly I would be too embarrassed to admit that the best I could do around town is 13 mpg.  :S   You really should try a Scan Gauge, they do not lie either.
If you or anyone else out there would like to go for a ride I offer the following wager:  We will take my truck to the gas station, fill it until the pump clicks off and then drive 100 miles in any direction you choose.  Returning to the same pump we will again fill it until the pumps clicks off.  The mileage will be as I stated or better.  Loser pays for the gas and lunch to include a beer or two.   :C