banditjojo2

Car started missing very badly. I changed the plugs, wires, egr, and map. The car still missed but only at high rpms. Sometimes it misses more than others. Sometimes it hardly misses. Would this be due to the optispark or would it be due to something else? If it is the optispark, do I need to get Gm replacement parts? Summit has one that is reasonably priced. Has anyone tried it? Does it work well? I also have o2 sensors coming back as codes. The dealership told me they were working. They said it was due to headers and Flowmasters. Please help.