Thanks for the input guys. It was the water pump...and a collapsed thermostat housing hose.
The impeller had broken clean off and in three pieces. One of those pieces, I couldn't find. I tried flushing the system....but it's just gone.
A couple of months ago, I took my car to the dealer to do some recall work. While I was there I asked them to replace the WP so I could avoid this whole hassle.
They said "don't worry, those things never go".
