Another 1995 S10 Heater problem

I have no heat (or little at times) in a 1995 S10 2.2L. Heater core was replaced 14 months ago, engine 12 months ago, thermostat 1 week ago, water pump 12 months ago.

When this first happened a few weeks ago, I flushed the heater core and found black thick anti freeze in it. Thought it was just clogged. Heat came back for a day. Since then I have flushed entire system and heat will work for a day then stop. Have not attempted to bleed air from system yet (just learned of it).

I am concerned about the water pump. I see no circulation in the radiator. I feel no circulation in the upper radiator hose. If I disconnect the heater core inlet and crank the truck, while running the water just sort of runs out slow. No pressure whatsoever. Water Pump maybe???

thanks GI Joe

Was the thermostat still in when you did this? If the water pump was bad, this truck would overheat like crazy. If the engine does not overheat, the water pump is fine. If flushing the system gets the heat working again, chances are the core or the engine is not as flushed as you probably think. As bad as you described earlier, you may need a chemical flush to clean out the gunk. I usually do not suggest this because it is hard on the seals, but in your case, I think it is warranted.

Yeah I left the thermostat in. Just a little too cold right now. The truck does not overheat at all. I was thinking maybe the water pump was failing, as in maybe the impellers are wasting away??? One more thing, I changed over to the regular green coolant many many years ago. The stuff in the heater core looked like stagnant anti freeze, like it is just sitting there. The coolant I flushed out last was very green and bright, not brown or thick. It was just black like this in the heater core.
Thanks, GI Joe