So to save me time and address my exact problem. I just changed the spark plugs on my 2003 CTS and after running okay for like 5 minutes cylinders 1 3 and 5 all started misfiring I literally don't know what to do. I have roughly 190K Km on it. The plugs I used are E3 Plugs. I've used them on all my cars. But yeah the help would be appreciated before I take it to cadillac tmr morning. Thanx guys!!