I'd recommend just going ahead with pulling the water pump. You'll be able to get the best snapshot of your cooling system that way. You'll be able to check if your divider plate(s) are in good shape, and you might as well replace your T-stat with another one in case that's an issue. Besides, you never know what a previous owner might've left you with (or without!).
It sounds to me you might not have adequate flow. If your divider plates are corroded away, it can cause the impeller to just spin around, making a whole lot of turbulence and no flow.
Feeling your heater core lines (if connected) can also give indication of flow.
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"...ridge reamer and ring compressor? Do they have tools like that?"
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