A friend is always complaigning about poor mileage, brakes don't last and his vehicles are always needing work. Yesterday I rode with him on a 100 mile trip, and discovered his problem. On the freeway he is always on the gas until he catches up to someone, then he pushes on the brake pedal, and repeated the process all the way between San Diego and Los Angles. The speed was always up and down, never steady. It drove me nuts. We checked the gas mileage and his Envoy with a six cylinder engine got 12 mpg in 200 miles. I now see why he goes through gas and brakes so quickly. And I was surprised at how much it bothered my being in that car. If we go again, I will drive my car or not go.