Fuel mileage mods and alternative fuels

With fuel prices soaring and no relief in sight I thought we could share our ideas and experiences. You know like what you tried, how well it worked or didn't work.

For instance I have a 2500 CRD Cummins 4WD truck, automatic with 4.10:1 gears in it. It got 14.5 or so MPG when I bought it. I installed a K&N air filter, without really noticing any significant improvement. I added LT315/70 R17 tires and got maybe .5 MPG improvement. Next I got a Superchips tuner, downloaded the tow mode and picked up 1 mpg. I tried the performance mode but my mileage got worse (probably because it's just too hard to keep your foot out of the throttle). Next I installed an EMS Off Road free wheeling front hub kit and saw an increase of .9 or so MPG.

So I spent about $3K for 2.4 MPG increase. Not sure if that was worth it but it is a significant gain. Next mod will be extrude honed injector tips, the fuel mileage ones but they aren't cheap either at $750 plus shipping and a $400 core charge up front. At least I'll get that back.

So let's see if we can help each other out and save some cash. Cars trucks, gas or diesels what have you guys tried?