God, I wish I was getting numbers like that!

My Bronco gives 11.5 when it's doing good. That's primarily city driving,
but highway driving is about 16.

Change out the o2 sensors, depending on the mileage.  As they age they
get lazy and it cuts down on the economy you can get when in closed
loop operation.

Most chips are designed to improve wide open throttle performance, not
exactly a way to get good economy.

Those are very good numbers for an auto. I had a '98 ranger w/ 4.0L 5 spd
extended cab 4x4 and got avg. 17mpg

I now have a basic 2.3L 5spd Ranger. I find I can get 2 or 3 extra mpg by
driving slower and pulling from a stop easier. Changing your driving style
may be difficult, but for me, if gas is going to be near $3 a gallon, that's
the was it has to be.
John