2004 pontiac grand prix

Bleed the trapped air out of the cooling system. There is a bleeder valve near the thermostat housing. It also seems to help having the car parked facing uphill while you do that, or maybe up on ramps. As long as there's air in the system you will have overheating problems.

did you end up figuring out what fixed it? I have 2004 gtp and when I got it the previous owners had let it get too hot idk how many times and therefore ended up with two blown head gaskets, had to have new heads and one valve was completely burnt. got ALL that fixed and a new radiator, thermostat and it's been back only 3 days on the road and had just a couple more times over heating since... sigh. i've checked the water pump and its fine but i've bled all the air out of the system and hasn't overheated since.

Sounds like you found the problem. Trapped air in the cooling system is the number one problem people have with these cars by far.

I feel like I have it bled out as much as possible, is there anything preventative I can do in the meantime to keep the air out?

No, once the air is out its out. It gets trapped in their during the refilling process. The cooling system is a fairly tightly sealed system so as long as you don't have a leak you will be good going forward. Just keep an eye on the coolant level for a while since everything is new, but you should be able to just drive it now. If it acts up again, check for air in the system again in case you didn't get it all out.