1985 300D Turbo Overheating.

I am in central Mexico getting ready to return to the U.S. and my 300D is overheating with coolant overflow. When I am driving on the highway the temperature stays normal but when I get into slow city traffic the car overheats and overflows. The thermostat has been removed. The radiator has been removed and sent away for flushing. The fan clutch assembly seems to be in good working order. All belts are tight. The problem persists. I am thinking it might be the water pump getting ready to go.
When I squeeze off the top radiator hose and release it I think I can feel flow. But nothing that I would describe as a pressure surge. Is there supposed to be a pronounced surge or just some flow? It's a pretty big hose so I think i should be feeling something more than I am. The water pump weep hole is clear. There is no squealing or any other unusual noise coming from the engine. If it's not the water pump. Are there any other places I can look for blockage. Any help will be greatly appreciated appreciated.
Thanks,
Ron