In my experience fuel economy is largely a matter of perception. I've tried just about everything, including a 203 t-stat, and while I'm thinking about improved economy my driving style adjusts and I get improved economy.

Funny thing is, when the new wears off and I get back to my "regular" driving style, my fuel economy returns to it's previous state. The nice thing about that is my truck got ~17 mpg stone stock, and now 176,000 miles and an additional 200 horsepower later......it still gets ~17 mpg.

The bottom line is....if you want better fuel economy you have to drive slower, feather the throttle, baby the rig....etc. etc.