Gas mileage

[Fourks]

So, I used to get, maybe 200 miles, giver or take a few from fill up to gas light trigger. Now I am getting 175 to 180 miles. I have changed out the air filter a couple times through this, a couple sets of tires from regular, to darkside and back to regular. I have around 55k on it. Is it a computer setting? Has anybody else seen this drop in mpg? It is not horrible, but it is a question to ponder.

Wonder if it could be a slow responding O2 sensor? Did you see the drop when you went dark, and has it improved going back to the correct tire? Also, have you added any assessories or increased the windshield height?