So recently I've noticed that my gas mileage is going down. For instance, I drove back to school today and my average was around 23mpg at 75mph... Normally it's at least 28mpg. I've noticed it around town as well. But on the highway the instantaneous mpg gauge in the cluster rides much lower than normal at constant speed. It has a K&N drop in filter with not even 5k on it. Any ideas guys as to why my mileage sucks all the sudden?