Fuel Injection problems of the 2006 Hyundai Tucson

Purchased a new Hyundai, Tucson, from monroe Hyundai a year ago. After a break-in period, I started checking the mileage. I quickly found out that no matter how I drove my car, the mileage didn't vary. One hundred miles an hour or 35 miles an hour and you get 22 mpg in either case. I took the vehicle back to the dealer on several occasions, and did everything they told me. A mileage study done by Hyundai resulted in the same conclusion. I've talked to other owners of the same model and they all have the same problem. Experts in the auto field have told me that the problem has to be the computer that controls idling, and the pumping of fuel has a problem. Hyundai has recently stated there is nothing they can do, and basically stated I'm stuck. I'm retired and I wanted this vehicle to last for some time. The dealership refuses to assist me in contacting Hyundai engineering, to discuss this problem. Please help! I can't afford to trade this SUV in, and I would like to see it repaired so my mileage is proportionate to how I drive. Generally 10 - 15% mileage difference should be expected between around town vs highway driving.