2002 1500 Ram 4.7 overheating

This p/u will run for a 1/2 hour at normal temp and then spike. I've changed cap, thermostat, overflow tank (cracked) and fluid. Cab always blows cold air. I bled system with cap off engine running, heater on high for a 1/2 hour. Still no heat and still overheats. While bleeding it I did notice the top hose wasn't real warm. I squeezed it several time to make water flow into overflow. It got warmer then and I had a bit of heat in the cab. The heater core appears to sit very high on the firewall so I thought maybe air is still trapped. I even but the p/u on jack stands to try and get the cap higher than the core. Nothing. Can the water pump be weak and not pushing water hard enough?? Other ideas?

waterpump broken impeller or plugged radiator