Is the P0300 the Only code you have ,
Does your scan / code reader tool have live data .,
Can you do a fuel pressure test when cold and when the engine starts to misfire .
Most typical issue for the problem you are having .
If the misfire is only ones the engine is warm as said above :
Crankshaft sensor . Known to cause problems when hot and not trip a Crank sensor code,
Coil , Very typical, remove and check for black burn spots like a powdery black spots .
It normally as coil issue if light load on engine causes the misfire .
Even though you have tested cap ,wires rotor if they have not been changed in the last few years i would do this anyway.
A P0300 code with no other codes is normally Ignition or fuel issue .
Still need additional information then please get back to me with the reply button, and not the poor or bad service, this way i can get back to you or suggest another expert if needed.
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Kind regards Greg.