It's funny...I just recently went through a similar situation and all I had done was replace my oil pump...it siezed (but not because of my car overheating) - thank God for Royal Purple motor oil!
Anyway, after fighting with my cooling system for a few days, I pulled my water pump and found a small hole in the steel casing. So, I purchased a new water pump and flushed my cooling system (with the water pump removed). After installing the new pump and before installing the thermostat housing, I filled my block with water, just to make sure. After buttoning everything up and adding antifreeze, my car runs extremely cool...even with a 180 deg thermostat. So far, I have not needed to use my electric fan - it is cool here in Texas right now...
Does your temperature surge or stay at a constant temp? If you remove your radiator cap, does coolant surge out of the radiator? One more often overlooked item...when was the last time you replaced your radiator cap? Just more questions to try and help....
Clay