yeah, that exhaust isnt the greatest, but it isnt gonna rape you on power liek the charts were above. the ecu could eb in limp mode though. are you sure the afc is wired properly? its hard to tell whats wrong without being there. other than that i would say get a conmpression test and if it checks out fine, go over the entire car again and just look for anything that could be wrong. i know you said there are no leaks, but check again. rewire shit if you need too. reset the ecu, etc. im sure its something small and stupid, you just havent realized it yet.