Did an 1,159 mile trip through Michigan's UP last weekend. I'm guessing that between myself, my wife and our gear, was hauling close to 500#. Overall mileage for the trip was just below 38 mpg. Best leg was 39, worst was 35, but that was climbing the "mountains" and long stretches in 3rd & 4th gear. Most of the highway driving was right around 65 mph. At one gas stop, went to 87 octane since there was no mid-grade there. Didn't notice any difference in mileage, but did feel a bit of a decline in acceleration, but maybe that was my imagination.