1994 Camaro Z28.

I know this topic as been talked non stop, over and over but i just cant figure out my problem, even after reading millions of threads about over heating. Its been bothering me so much that if i cant figure it out by summer im just going to have to sell it. Heres my problem and what ive done so far...

When I am idling my car over heats. On hot days it doesnt take to long for it to get to the red. I had to incidences where i had to pull over and turn my car off. Once i popped the hood i looked and coolant was pouring out of the over fill tube. Both times the engine light came on and the temp gauge was as far as it can get into the red. It ONLY over heats while idling. When i take off from the light and drive a little ways it'll go back down to normal temp ranges.

The things ive done was, one replaced the thermostat. (didnt help) then i went to a shop and had them do a radiator flush. I thought maybe it was clogged somewhere. Still didnt work. Ive checked my head gaskets and there ok. WHAT SHOULD I CHECK? DO? SELL?

 

And i forgot to mention that i took it to a place for the over heating problem. They did a whole test with the fans and told me everything checks out to be ok

 

Has the coolant been bled correctly? It's normal for these cars to heat up when you come to a stop, but should not get in the red. Take the radiator cap off, when the engine is cold, and check to see if the coolant level is up the the bottom of the filler neck. If it's not, put some more coolant in. Keep checking the level, until you don't have to refill anymore.