All winter long my average gas mileage has been 12mpg. It would vary between 11.9 to 12.2. Since my last 2 fillups of Shell 93 I jumped to 14mpg. I haven't changed my driving at all. I live 5 miles from work and drive fast all the time. Could the gas stations have changed to a summer blend, or am I just crazy. I've got about 8,500 miles on it and its an 04.