Hello everyone! I have a 2003 Grand Prix & I'm currently getting the engine rebuilt. I want to upgrade to a brand new SLP header & cat kit now that I have the chance. Most answers on this emissions question seems to point the computer and not the headers themselves in the ability to pass the emissions test. I've heard some muffler shops say it should pass, but I'm looking for anyone who actually knows firsthand for sure. I'd hate to drop a $1000 on parts & then I can't drive my ride. Thanks!