running too cold

I think your water pump is fine. If it wasn't, you would either be overheating or leaking coolant. All the slants I used to drive ran cool winter & summer, just like you describe. I still recommend you block off some of the air flow, try 1/2 and see how it does. Watch the gauge and if you get uncomfortable, remove your blocking.
It's not unusual in cold weather to see big trucks, school buses and other heavy vehicles have most all of the radiator blocked off like this.

But I sure wouldn't change out the water pump.
C