yea ive noticed the fuel mileage has decreased a good bit. but as for kr goes before headers at wot it was reading 4.0 to 7.0 i just kept out of the throttle until i got the headers and it went to .2 to 2.9. thats alot better i must say. you would think the pcm could adjust for this or i may not know what im talking about. still new to this platform.