I find that I'm having a hard time keeping my fuel economy above 40mpg. At least according to the DIC. Commute is 90% highway, about 20mi, and I drive like an old man. Each tank seems to be a little lower. The only thing I can figure is that it's been quite hot and I'm running the AC full blast. Is that really enough to have that big of an impact on fuel economy or should I bring this up at my first oil change? Only 3k mi on the odometer right now.