Poor Fuel Economy

[baloneyhomie]

Hi everyone, I've had an account here since I purchased my Marauder back in January.(I'm not much of a message forum guy, I usually stick to the /r/Crownvictoria subreddit), I have a question that I feel y'all would be more qualified in helping me out with. To start, this is a 2003 Marauder that I purchased with only 35k miles, and have put about 2.5k on, it is now at 38,7xx miles. As far as aftermarket parts goes, I have not put anything on since I purchased it although it does have a Reinhart performance chip, an electric water pump, and underdrive pulleys. Now, I always get 10MPG in my town no matter how I drive it, whether or not I have the performance chip "on" or off (in my specific car the previous owner had set up a rotary dial that allows me to switch to and from the performance mode to what I assume is the stock tune, and a valet mode. The blank selections act as a kill switch of sorts, but I digress). The only time I get even above 12MPG is when some of my driving is on the highway, but I rarely ever get on a controlled access road like that. I have checked the tire pressure and all four are at the recommended PSI, I have changed the oil as of 2 days ago (not sure if that could affect it but worth listing I figure), the transmission fluid is in good shape, but I routinely get 200 miles or so out of every tank (I usually fill up when the fuel light comes on because I hate taking chances with gas, even if I'm in a pretty urban area) even if I have the performance tune selected the entire time, or the stock grandma tune selected. I really cannot think of any way that the only other thing that might affect the fuel economy (the underdrive pulleys) could affect it so much so as to bring it down to barely double digits. For context, I live in Georgia and my area is basically a pancake besides some very soft/rolling hills. It's not really stop and go hence my usage of town instead of city. If anyone has any suggestions, please put em down below. I can survive with 10 MPG since I don't drive often but if there's an anomaly on this car then I'd like to get that fixed or looked at if it's out of my area of expertise. I can provide pictures of stuff if needed, please just give me the word. Thanks.