The problem was the HPOP. I pulled everything off the top, and replaced all the o-rings, and the STC fitting. I tested the system with everything off, and it definitely was the STC fitting. Replaced it, retested it, and everything was air tight. Took the opportunity to install 4" MBRP turbo back exhaust (cat delete) and do my own EGR delete as well (pics to come). Got 'er runnin today, and boy am I happy. When I had the manifold off, I soaked it in parts cleaner overnight, and now the engine is a LOT louder than I remember. No more insulation inside the manifold.
