Yes. I'm crossposting. Is anyone really gonna complain? Seriously?
I did the timing chain, exhaust cam, injector rebuild kit. It sounded alright but needed a new IAC after being on blocks for months. That fixed the emergent vacuum issue, but then I replaced new oil pressure sensor and the gasket on that whole module (for the umpteenth time). Should be good to go, right? No. This is when things really went south.

It had sounded like there was maybe an exhaust leak or something scraping or sputtering only when the engine was under load and initially at high RPMs, after the initial round of work. But now it sounds awful. It is misfiring (Kmanager says on all for cylinders but only occasionally and just a few seconds after throwing an MIL). An additional clue is that I got a VSS malfunction and the RPMs and Speedo have at least once moved together while stationary.

I got nothing on the VSS, but could the noise and misfires be a result of a clogged cat, and an associated exhaust leak be the cause of the noise. WTF? HELP!