What type of fan do you have now?
Is it shrouded?
Is it mounted within about 1/2" from the radiator?
Does it come on at what appears to be the right temp?
Do both the upper and lower radiator hoses get hot?
Is it possible somehow that due to your pulley configuration, your turning the pump backwards?
Can you look into the radiator and see a good strong flow?
Hang in there, you've got the best minds in the industry thinking about this (US)
Ed