Chevy 6.0L runs very rough

2000 Chevrolet Silverado 2500 LT, ECLB, 6.0L, 220k miles. Runs very rough. Currently showing codes P0300 & P0101 via Torque Pro App and bluetooth OBD2. Ran searches and checked the following: fuel pressure regulator - good, fuel filter - replaced, fuel pump - replaced a few months before engine started running rough, milky goo on underside of oil fill cap -> intake manifold gasket leak - removed and replaced intake manifold gasket - thorough cleaning of throttle body & intake manifold as far as I could reach, checked cam shaft position sensor, checked throttle position sensor, pulled and power cleaned all fuel injectors, checked for vacuum leaks with smoke - replaced 90d elbow at top of intake manifold, replaced all spark plugs, checked all O2 sensors. Here is a link to the video i took of the engine running.
drive.google.com/file/d/1wsqkIYVNBwVCkDf...ECS/view?usp=sharing
Let me know what questions you have. If you think I should recheck something, I can do that. I don't have a shop grade scanner.

sounds like a rocker arm is making noise

You could put a vacuum gauge on it. But I agree sounds like rocker arm. You can use a long screwdriver and put your ear to it and stick it on the valve covers to try and figure out which one to pull first.

Or do this.


cant say on how it works as I use a stethoscope

I found this on youtube - it sounds very similar

The poster said that the result was bad main bearings, but does not state how it was confirmed. Other videos show badly chunked valve lifters and cam.

I'd suggest a manual power balance test to first ID which cylinder is misfiring. You can either disconnect injectors one at a time, or coils, doesn't matter. You've found the misfiring cylinder when you disconnect something and the engine doesn't seem to notice. While doing that test, you can also listen to that noise and see if it gets better or worse with a cylinder disabled.

Start watching at about 1:20:



A relative compression test would also be a good idea. Easy, too, because Chevy has clear flood cranking mode. No scope needed, just floor the gas and crank the engine. Listen for a 'skip', or other abnormal rhythm in the cranking sound. If Cheryl and gav09 are right about a rocker arm, then you'll definitely have an irregular cranking sound.