I drive a 2007 Pontiac G5 2.2L. It has a cylinder 3 misfire, and whenever it does have a misfire it shifts hard between 1-2 and 2-3. When you cold start it it'll idle fine for a few minutes and then you can hear the misfire start, it'll start making weird noises and idling really rough. I replaced the plugs a couple months ago (they were cheap plugs.) I also got the code ran again and it had a O2 sensor code, coolant Sensor code and the misfire. I replaced the coolant sensor and replaced the cylinder 3 coil. And it was fine until about 3 hours later i got in it and it started missing again and shifting hard. I'm really confused as to what it could be, I do know that it needs a catalytic converter as well. Any help will be greatly appreciated!