EcoTec 5.3L V8
I have 2016 Sierra 4x4, 5.3L. A couple years ago I did the cold air intake and cat back exhaust, and a Superchips programmer. Just recently I added Stainless Works long-tube headers with performance cat/Y pipe. Fired it up and the check engine light came on, kicked up code PO420 and PO430. I put...