You’re asking a lot. The two concepts I know of to read up on are aeromodding and hypermiling. You could also go cash for clunker or buy a scooter or motorcycle, assuming the cost of the bike is less than your normal fuel cost. A fifth option would be to reduce the weight of the vehicle.

Here’s a thread on hypermiling a Durango— http://ask.metafilter.com/56550/Getting-better-gas-mileage-out-of-a-fuel-hog

Get out and push?