Head gasket or Limg??
 

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

head gasket. change both.

Inspect for external leaks as well. That's how I figured out that all I needed was the LIM. I could see it dripping.

I agree that most likely the headgaskets and lower intakes need to be replaced. I would advise that you only use AC Delco gaskets, and follow their updated torque specs.

Another possibility is that the heads and/or block are cracked or warped. If it were my car, this is where I would considering doing a 3500 swap.