You forgot the easiest way to cut fuel costs by a whopping 50%, not 2 or 3%.....
TRADE THE V8 SUV in on a medium sized 2WD sedan. One gets 13mph, the other gets 26mph.
Unless you live in an area whre 4WD isn't a status symbol but a necessity. Our 4WD Subaru station wagon goes everywhere and gets 34 MPG driving locally, which is mostly back roads. We never checked the highway mileage, but imagine it's better. In addition, newer SUVs is a bit over 20 MPG, 2006 estimate.