i have a TrailTech Vapor on mine. Gives me a speedo, tach, odo, and water temp. Cant beat it!
As far as mileage goes, i figure i've been getting about 35-45mpg out in the desert.
As far as tanks go... thats a 4.6 gal on there, i have the factory 3.2 and a larger 6.6 gal tank