Cooling system woes

Hi gang, just did a rebuild on the 5.0 last week. Had to replace the head gaskets for a leak, and add some other goodies that I had been waiting to do for a year now. Now I got my 30# injectors and mass air flow paired up, and the Trick Flow Track Heat set up is running great. Only hang up, I can't seem to get all the air out of the cooling system. I have installed a high flow aluminum water pump, new motorsport silicone hoses, and an electric fan with thermostatic control. However, upon warming the car up, trying to get it to operating temp, btw thermostat is 180 degrees and is the one I have been using for the last year and was working last week, I build pressure in the system and eventually start spewing coolant out of the funnel I have on top of the radiator. It acts like a huge air pocket is trapped in the system. If I plug the funnel, wait a few mins, the pull the plug, the coolant is sucked back in. I think the thermostat isn't getting a chance to open before the coolant in the radiator gets too hot. Anybody got any tricks for speeding the process up? I usually never get these problems on the imports I work on, and I don't recall having this much trouble last year after I did a rebuild. Thanks for your help.

Tried the nose in the air trick, also pulled out the "known good thermostat" or so I thought it was. Tested it in water and didn't want to open. So I installed a new one, Stant super premium, 180 degree, ran the car. Got up to operating temp, fan working, infared thermometer showed 185 and the thermostat opened up. However, after a while of idling with my funnel on the radiator, eventually pressure built up, coolant temp guage spiked, and the spewing began again. It's like there is a stubborn air pocket in the system. I think I might pull the thermostat out tomorrow and run without one and see if the air comes out of the system. On a side note, I used a set of cometic Trick Flow head gaskets this time, the number says it is for my application, used matching intake gaskets and trimmed excess that was in front of cooling passages. Made sure the head gaskets were installed in the correct direction, as well as the thermostat, spring facing intake, new high flow water pump spinning counter-clockwise. Only cooling factor not changed was the radiator. After revving the engine today for about 2 mins straight, the headers started to glow red at the collectors, now the engine was already at operating temp before the revving began. Is this normal? Or is the cooling problem affecting the heads and the exhaust gas temp as well? I had stock headers before and never noticed this, I have Flowtech headers now. Thanks again for all of your help.