I posted a week ago about installing headers, replacing my o2 sensors with new ones and suffering from a "loaded up" feeling engine until about 4,000 rpm. I thought maybe the ECU had to re-learn the new sensors, and the problem would correct itself. I still have the problem, and now sometimes it dies upon letting up on the gas, it sometimes catches itself and idles fine. The check engine light came on today and the codes were P1204,P1205,P1206,P1300 all indicating a misfire. I checked plugs and they looked fine, they were replaced less than 1000 miles ago and, at the same time the valves were adjusted. I'm not sure what to try next. Any suggestions before I give in and take it to the dealership? Thanks.