[azraelswrd]

-Corona

If nothing has changed in terms of equipment and driving, and only in fill-up location then it is not a leap that the new gas is not as pure as what you were using before. I've read enough reports that gas with ethanol added is less energetic than just pure gas.

I always try to go and refill at the same station. Look around and see if there is some sign that says "Up to 10% ethanol". I believe states are pushing for mandatory notification (which means not all pumps say if they have E# or not).

If there's nothing wrong with the gas, then it could be something else in the engine. I won't pretend to be a mechanic but when was the last time you had the car/truck serviced?

Yes, heavy A/C usage will hurt your fuel economy. If you must use it, the best way is to use it only on highways and in short bursts with the air on recycle. Turn off the A/C once you feel cool enough. Turn it on once the heat gets too unbearable. At slower speeds, windows open will be better as the drag won't be as bad. Full A/C vs low A/C is a slight difference but it depends on the specific parts in your vehicle and how long you're running them. Not all compressors were created equally.

If you had some way of seeing your instant MPG or gallons/hr then you'd know for sure which way is better or worse. Assuming you're in the 2005 Civic, a scangauge can fulfill this need of instant feedback.