What up, so I've recently put on invidia catback mated to a stock dp and have noticed my mpgs dropped about 1.5-2. I have a 2011 wrx Cobb stage 1 + aem. It's been about a month now and consistently around 17.5 vs 19 or so before changing the catback( lots of city driving). Any advice/help would be greatly appreciated to get this back to normal because this seems abnormal. Thank you.