Sounds like air in the system to me too. I had a similar problem this week. Even if you have tried to remove the air, sometime it takes several attempts to get it all.
This is what I did and it worked.
1) Mark the level in the expansion tank for reference. Then loosen the expansion tank by removing the black plastic clip on the front, and the 10mm screw on the engine side. Disconnect the sensor clip on the bottom. You may also have to disconnect the large hose clip securing the hose to the wheel well.
2) Follow the line from the tank to the intake manifold. There is a nipple on the top and the large 2 inch hose to the front. Remove the small line on the top.
3) Put a rag around the nipple.
4) Squeeze the 2 inch hose until coolant spits out of the nipple (this may not happen)
5) Lift the expansion tank as high as possible. This should force any repaning air out of the system. .
6) Reinstall the expansion tank and reattach the hoses.
7) Fill the expansion tank to full.
8) Start the engine and let it run until it reaches temperature. I went for a quick drive to the grocery store. When I got home, I checked the level in the tank again and had to add a bit more fluid.
9) If the problem persists, repeat after the engine cools. After 3 attempts, I would say you have another problem. The T-stat may not be opening.
I would imagine that if you lift the tank and no fluid comes out, and your fluid levels are normal, that would be a good indicator of a blockage.
It is possible that the repeated over heating has damaged the T-Stat as well. If this doesn't work, I would have it replaced.
Watch these for details on how to burb the system. It helped me a lot.
Rad Air Removal 1 video by GSStage1RedSky - Photobucket
Rad Air Removal 2 video by GSStage1RedSky - Photobucket
And check this thread
Is there a DIY on how to replace 2.0L Turbo (LNF) thermostat out there?