[DavidV_]

Hello, new member here so forgive me if I do anything noobish . I have a blue Alero 3.4 with just a little over 114k miles on it. For awhile it’s had issues overheating, sometimes to the point where I’d have to pull over to let it cool down a bit. Recently I decided that I should do a coolant flush, I drained old coolant (which was quite brown), changed thermostat and coolant temp sensor, and filled her up with water and Prestone Flush + Cleaner. I turned it on and it began to act strange after awhile and a CEL popped up so I scanned it and had a p0306 misfire code, it got late so I left it for the day. Today, I turned it on and it struggled quite a bit to start and sounded kinda bad so I decided to check the CEL again and a p0300 code came up. I checked the oil and I got quite worried when I saw that it was milky. The head gasket was replaced a few years ago before the car sat until I got it as my first car. Could this be another head gasket issue or a limg? Car would use a lot of coolant and had bad gas mileage