This 2000 Intrepid 2.7 autoI have has an over heating problem, I noticed there is an endless amount of air in the cooling systemthat I cant bleed out. I can drive the car on the freeway for 30min with out any over heating untill I get off the off ramp. The cooling fans are turning on.

The car passed the block test.
Thermastat and rad cap and water pump were replaced.
Runs and idles great untillit over heats.
The engine was rebuilt less then 5,000 miles ago due to spun bareing.

Its been to 2 repair shops and they cant figure out what is wrong with it. Any one else had this problem before?