You must remember that you are having to move 6,000 lbs from a standing start every time you take off from a traffic signal. Also you must remember that it is 60 year old technology. And if you get to highway speeds, the old girl is not very aerodynamic. Your fuel economy might go up a little once the engine is broken in, but I wouldn't expect a whole lot more. I think you are about average for stop and go. Our 2 ton GMC bob tails used to get around 5 when we were hauling gasoline with them.
