Real Bad Gas Mileage!

mazda cx 7
Gas mileage is not bad in my 2007 cx 7

I've had my CX-7 for two and a half months now and i love the way it drives but, I consistently get real bad gas mileage around 12 - 13 miles per gallon. What's the deal? I drive approximately 50-50 city to highway not too heavy footed either. What would cause such low mileage? A/C has been on pretty much all the time, could that be it? I use mobil super 93 octane, could the 93 as opposed to 91 be it? any suggestions would be great. Thanks!
Got ours a couple months ago and have no problems with bad gas mileage..
2007 mazda cx7 fwd
Don't know how good it will work, but has a computer chip that is supposed to boost HP and increase mileage. I am going to install pretty soon to give it a try. Anyone else tried them?
Mazda, CX-7 2008 2.3L Turbo
Update on my car. My dealer just told me that my car was reading high in carbon. So they "de carbonized it" and told me to just drive it normal and check the gas mileage at the next fill up. I hope this works. I did noticed a lot of wispy white smoke coming from the exhaust after I turned the car off. We shall see if this helps with the gas mileage!
Did the decarbonization fix the issue? (by the way, what has to be decarbonized)? I am getting ~11 MPG! had the dealer clean the throttle body, however I see no difference..