I can't figure out why...........

[WRMZ71]

I can't figure out why my dang engine keeps on wanting to overheat. It's a 350 with a .488 .510 cam, edelbrock aluminum intake, holley 670 street avenger carb, and flowtech headers. It's got a recently new heater core, brand spanking new 4 core radiator and a 190 degree thermostat. That and I got an 16" electric fan along with the regular fan on the engine. I currently don't have a shrowd on it cause the one I had before would not work with the new 4 core radiator. I was thinking I had gases passing through a bad head gasket and pressurizing the coolant system but i checked it out and I didn't have any. I'm thinking water pump might be weak, but when you fire it up and look in the radiator the water goes down just like she ought to. Anybody got any suggestions? It just cannot handle sitting in traffic for nothing, and i'm talking like 5 min when its 50 degrees out and she's getting up to 240 already.