01 Jeep Cherokee Misfire Codes but no symptoms

My dad has a 2001 Jeep Grand Cherokee 4.0 with the misfire codes P0300, 301, and 302 but has no symptoms of a misfire, it runs perfectly smooth. He’s seen other misfire codes previously but those are the ones I saw with my reader. The car also has P0135 O2 heater malfunction and P0171 engine too lean codes. I’ve heard that the misfire codes could be false reading from the bad O2 sensor. It also has no symptoms of running lean, no hesitation on acceleration and all the plugs looked good. Could the bad O2 be causing that code as well? Any thought?

Thanks