Thermal issues, aka over heating question

[rkleypas]

I'm sure it's something real simple, and hopefully someone here can help. I've been having over heating issues since the Power Tour. LS7, twin e-fan Be Cool radiator. Gauge is showing 250 degrees after idling five minutes. Fans are running and temp keeps climbing. The funny part is the lower hose and lower part of the radiator aren't hot at all. There are some black flecks in the anti-freeze. Bad water pump? Thermostat? Air bubble? The cam was swapped to a milder one before the tour.