I installed the K&N replacement air filter on my 2008 Bullitt yesterday. I was averaging 18 miles to the gallon before the swap. Right after the swap I reset the numbers (I do this once a month). I logged in 100 miles on the new filter and average at 13.5-14 if I drive normally without too much revving. Is this a known issue? Should I just put the stock paper filter on? Does the Bullitt need more time to figure out its getting more air and needs to adjust the fuel supply?