About two months ago I installed the scan gauge which I purchased through Tone. This gadget will give me everything one can imagine, especially MPGs at any time. So for those with an interest in why they are getting the mileage that they are, here are some stats I have taken while driving for the last two weeks. Bear in mind that all figures are still approximations as I am guessing inclines and declines. I use the Nitto tires hence have calibrated the scan gauge for a 9% increase in tire size:

on frwy flat 65mph = 20mpg
on frwy flat 55mph = 23mpg
uphill grade 65mph~3% = 15mpg
downhill grade 65mph~3% = 34mpg
uphill grade 65mph~6% = 9mpg
downhill grade 65mph~6% = 45mpg

City driving is where I noticed using a lot more fuel. Hard accelaration will cut into your fuel use very quickly. I add 9% to the mileage per gas tank to make up for the tire size. On 65mph in cruise control, I can average 19mpg if it is mostly flat. The hills cost a bit of fuel. Window is up for the most part and AC was off. I believe that a lot of us tend to punch our VX, fast take-offs and speedy driving. This will cost you. I drove a little more gentle for a while and ended up putting 300 miles on the tank, where I filled 18 gallons averaging 16.6 mpg. This included at least 50% city driving.