if you have a new waterpump, did you check to see that the divider plate is as close to the fins as possible? it seems the consensus that tweaking the plate closer can help alot. there is also a pump with a cast iron impellor which is supposed to be better. do a search in tech help on 'divider plate' and you should get some good hits.

once it's running cooler, the antifreeze will still spew out a little if the radiator is filled all the way to the top.