Its not the o2 sensor standard ones dont read after 3000
step one borrow an air flow and try that first as it wont cost anything the air flow meters do sh*t themseleves but i think will find the new exhaust has allowed the engine to brethe and the boost hads more than likely picked up 1 or 2 pound s1 coils are really sh*t even if you replace and regap the plugs it proabley wont fix it get spit fire coils and ngk plugs and that will do the trick