(iv got a 01 chevy blazer 4.3l iv got a p0300 code (radom missfire)

you may having somebuild up on the back side of the cyl head valves,try cleaning the with the gm type injection cleaner that you run thru the fuel lines not the cheap stuff

You just did what? You have the specialized equipment that hooks up directly to the fuel rail to run the engine on the cleaner with the fuel pump disabled? . My bad I didn't read your post throughly, sorry. Did you replace the distributor cap and rotor?