I have a 2007 Honda Hybrid Civic. The first couple of years of driving, I had gas mileage that averaged 40-45 mpg. Starting with this last winter, the gas mileage dropped by 8 to 10 mpg. I avoid ethanol additive gas (when I know that it is ethanol). I have also bought higher octane fuel, but still the mileage is much lower now than 2008. Why? Or, what should I do to help?