I usually fill up the tank when my trip hits 200 miles, which is then reset every fill up. My gauge isn't that accurate. A few months ago I could push it and get up to 250 miles on a tank. Last week I only got 180 out of it before I put 14.x gallons back into it. I didn't mind too much cause I ran the hell out of the car at the track and had quite a few other races. This week I'm at 190 and I need to fill up again. I didn't go to the track, no street races, and actually more highway miles than usual?

Why would my gas milage be getting worse? It's not just a spur of the moment thing I noticed, it's been happening gradually over the past 2-3 months. I don't have a clue? No new mods, nothing has changed, unless you count an alignment.

 

When was the last time you replaced the O2 sensor?
tune-up
tire pressure
if the alignment was done wrong it could actually affect your gas mileage and wear your tires prematurely.

 

Tune up less than 3 months ago.
New O2 sensor installed with header install, august.
Tire pressure is normal, if not just a tad low.