Seems like a blockage to me...... on the other hand maybe your temp sensor is faulty and giving you false readings. If you can pick up a laser thermometer check different areas of the heating system for differences in temp. Also open your rad cap (not while it is super hot) and watch the flow of the water when you rev the engine. If the flow picks up then your pump is probably good. Add coolant as necessary.
I like to stick a hose right into the filler neck with a wet rag tightly wrapped around the tip to seal it up (sort of). You may have to hold it there but turn the hose on and open up a connection somewhere. I find a heater hose to be a good spot to use. Watch the flow out the hose. Maybe try another hose for the coolant/water to escape and once again watch the flow. It's not high tech but if you do this in a couple spots, you will soon see if you have a blockage. You can also pinch off or cap off one side of the connection that you have open in order to force the flush out one side and then the other. Hope this helps you narrow it down.
Good luck
