 I bought my sonata new in 5 of 09 and from the very begining had very poor gas mileage and a shifting issue with the trans at about 38 to 40 mph and around 15 to 18 on the rpm gauge when I brought it back to the dealer for service I was told it was how the car was supposed to drive and that there was nothing they could do to fix the problem except to flash the computer and then reset it . I was also told that it was the way that I was driving the car. now that I had the computer reset and the trans flashed I now get 15.9 miles per gallon to a full take of gas and was told that it was because of the winter gas that is now out on the market well to that I say B S 