air bubbles in overflow?

[slider_buck]

it all started the other day when i was going to work and the thing quit putting out hot air from the heater and got hot. when i seen the gage going up to about 260 i pushed in the clutch and killed her and coasted it up the road to a pull-off. i though for sure i had a blown head gasket because of air bubbles getting in to the overflow bottle so i tore it down and sure enough #6 and #7 blew. well i got it all back togther and still have the same problem. i have a new 3 core radiator, new 180 stat, new hoses, new water pump. what else could it be. the funny thing is that if i set there and keep it reved up to about 3 grand it will stay cool but when i let it idle it will start to heat up. then every now and right about when the stat should open up the temp gage will climb up really quick and the coolant will start to rush out the radiator, it will blow about half the coolant out when it does this. i did both a leak down and compression test which were ok. i'm stumped.