P0300 random misfire

Before all this happened my engine was running very rough and had the coded p0401. Eventually it was both p0401 AND p0402, then it was towed to my garage to get fixed.
I did the spark plugs, wires, coils, timing belt (not off or skipped tooth), water pump and cam/crank seals, PCV valve, and valve cover gasket.
The code of p0401 is not long showing up currently, along with p0402. I start the car no problem, but it’s running about 1,200 RPM's, I push the gas and the vibration gets worse and then the RPM will start to severely drop to 500 and stall out if continued pressed, or I let go and the engine will pick back up to “1,200 RPM's”

The compression I would assume is low due to this so the engine is trying to make up for it.
My battery is 6+ years old (could be newer but I’m going off the sticker on it) but reads a voltage 12.36 volts when the engine has been turned off for less than 1 hour.

I have not vacuum leak tested the engine yet but I don’t believe it’s the cause to my problem. Carbon and build up would be more likely possible, however mostly everything is original from 1997, or Toyota OEM replaced parts.

This is a battery issue or could I have further issues internally or a likely vacuum leak?

And would replacing the VSV module switch behind the block help in this case?