My mpg on a fill up was originally around 300 and now shows around 330 miles. Seems like it's creeping up every fill up. My mpg have been around 21.X as well driving mostly on sport mode. 20 inch rims on stock tires.I had a similar experience with my new 1958. Drove five hours to the Mountains on Friday and five hours back on Sunday. I switched the driving setting to “economy” and it averaged a little over 21.8 miles a gallon on highway going 70 - 80 mph. My only complaint of the vehicle so far is that, as you said, the gas tank is way too small. When I fill it up, the total anticipated mileage before empty states that it is around 315 miles.