Unique-ish Cooling Issue on my GTP?

Update. I went through the bleed process Scotty recommended. I took the rad cap off, started the car (I watched for bubbles too, in case a head gasket issue had yet to manifest, but no bubbles or level rising came... yet) and I let the car warm up. I kept checking the top hose to see when the thermostat opened, which it did at 180, then I let the car heat up until the fans came on at 212, and then before i could open the bleed screw, coolant suddenly started gushing and gurgling out of the radiator, white with bubbles, and then suddenly stopped. About a quart came out. I filled it up again and waited, but it didn't happen again, and the temp went back down to about 206 and the fans turned off. So then I bled it from the bleeder and only coolant came out. No bubbles.

I watched the temp for a few minutes while the car idled. It just kept bouncing back and forth between 203 and 212, when the fans would kick on.

So what happened here? Did I find my air pocket, or did the heat just boil my coolant for a few moments? Is 203-212 normal for idle?

Likely you did.

I always take the thermostat housing off when I do full flushes or replace parts, because the LIM is the highest spots and filling from there makes it a breeze.

Just over 200 at idle is normal with minimal to no airflow across the radiator.

sounds like it burped finally. tomorrow morning check the rad level ice cold, if its low top it off. fill your over flow to the cold line too.

I think it burped. I took it for a drive last night. It was about 70 degrees out, so cooler than other times I have tested it. However, I was able to make it up the pass I was trying to do before. The temps held at about 208 as long as I kept the speed up to 35-40mph. When I stopped a few times and started up again, the temps would climb to 217 and then slowly come back down to around 208. I find these temps for a mountain climb to be acceptable, but I still have reservations since it was dark and 70 degrees out instead of sunny and 100. It should be sunny and 85 degrees today, so I'll try it again and see if I get similar results.

I tested the cooling system again today. It was 80 degrees out and sunny. I drove a different pass, more winding and steeper. Its a 5000 foot elevation gain in about 20 miles. I averaged 25 mph with a lot of slowing down for switchbacks and uphill acceleration. The Temps averaged about 220, with the highest briefly at 228 (really slow and really steep), but the fans went on high and the temp dropped to 215 rather quickly as I continued to climb. Around town is 190 to 200 now. If these Temps sound about right, I'd say my cooling issue is solved, except for the small LIM leak I think I have, which I will take care of as soon as I can afford to do all the mods at the same time. Thanks everybody for the help and input!