With the plugs out, trying to turn it over sounds fine. everything seems fine, I have full view of the camshafts and they spin and are not out of place.
So you were driving it with only 3 functioning spark plugs? That would explain a lack of performance, but the CEL would have come on, and probably would be blinking.
A 150 PSI is a sign of wear. A 180 is fine. The general rule of thumb is compression ratio X 20 at sea level. Altitude, barometric pressure, humidity, engine wear, etc also has an effect. It should run good at 180.
Maybe the catalytic converter is plugged up or there is some drivetrain slippage.
It sucks to not be there with you because none of this would be a mystery anymore… Something is out of whack that should have been caught earlier and its impossible for us to guess from our computers what it is…sometimes its something you cant believe you missed.
The spark plug threads… if you are sure they werent cross threaded prior…how do you account for the “mushrooming” of the end of the plug? which subsequently “wrekd” the threads when you pulled the plug? That needs an explanation…dont move forward till you know.
You are missing something obvious… I dont mean to sound like a jerk but…when you do this stuff over 30 years you have made a mistake or 1000 in that time and learned a lot of ways things can get sideways.
I dont like that spark plug…what wrecked it…something did… is the rod of that piston letting go? A rod bearing? Allowing the piston to hit the valves? or the plug? I think all you need to know…involves the cylinder with the ruined plug.
Thats what i think…way over here at my computer desk and not onsite based on the info I was fed.