Yeah I went and clocked my gas milage today. Today my car decided it wanted to get 13mpg highway. I cannot figure out why it gets such bad mileage. I just replaced the fuel filter. Air filter is good. All fluids are good. Tires are full...

I am really thinking of finding another car if i cannot figure out what is wrong...

just a thought: one of your sensors is bad or sending a wrong signal. possibly the o2 sensor. OR, one of your injectors is leaking and pouring too much gas in. maybe even carbon buildup in your manifold, which wont allow the proper airflow. could be several things. things i would check when running rich: vacuum lines, pcv valve, map or maf sensor, o2 sensor, some kind of blockage in your intake, lower manifold gasket, egr valve and gaskets, etc...

Before you rule out anything, check one common problem: the fuel level sending unit. I've seen a slew of vehicles with bad units and the customer complaint is poor mileage. Unless you actually keep track of the miles driven on a full tank and how many gallons you fill up at next, it's incredibly misleading.

Sorry if this sounds like a "duh, common sense" answer, but we need to rule out a bad unit first. No sense in plopping down a grand only to find it was a sixty dollar part you can put in yourself.