Had similar issues recently with my wife's GranPrix. Replaced the entire ignition system. It was getting random misfires around 4K rpm. Long story short it turned out that the cat was stopped up! You can read more here if your interested. http://www.grandprix.net/cgi-bin/ultimatebb.cgi?ubb=get_topic;f=1;t=005019;p=0&r=nfx Britt