Has anyone found a difference in their gas mileage caused by the brand of gas they are using? I am not real happy with my gas mileage right now -- averaging about 24 with 40% highway, 60% city and the dealer tells me that the two causes are the winter blend gasoline and also warned only to use name brand gas. In our area we do have some Gulf and Sunoco stations but the only high tier gas in the area is Shell which is usually about 20 cents more per gallon for regular. We also have many Supermarkets and convenience stores such as Wawa, Turkey Hill. 7-11 etc. who sell generic gas. The dealer said do not use these as it will reduce your mileage. I have been using a combination based on where I am when I need gas. Just wondering what anyone's experience has been with this,