5.2, Very hot in cab, radiator cold.

[mrspooks]

Hello,
I have a 97 ram 165000 miles with a 5.2 that will not pump water through the radiator.
Initially I replaced a leaking water pump with no issue. Over time realized that no matter where the temp selector switch was placed the heater would blow VERY HOT air. Initially I thought that it was a vent door issue but upon checking I found that the radiator was cold even when heater air was HOT.
I changed the thermostat to no avail. Radiator does not appear / test to be blocked. ( I occluded outlet outlet filled with water removed occlusion and radiator flushes quickly with 10" gush.) Removed upper hose and only get a small stream out when engine is hot.
I have removed and checked that the impeller is attached to the shaft and the belt tensioner has been replaced.
There is no sign of a blown gasket, no bubbles in coolant no "milk" in the oil.
Any help or ideas would be greatly appreciated.
Thank you.