Hey Chris, I have recently built a stroker and I redid my exhaust system with some torque tube headers and all. I removed the 3rd cat, and bought new ss pre cats. Anyhow, it seems to be running good. But I cant help but think about someday removing the front cats, and depending on how it goes, I might leave um. But I would like to be able to tune this rig. Anyway, long story short, too late, what is with the credits? I don't really understand why a guy needs to buy them. What's that all about? Thanks for all the great info!