Cant believe your still having issues!
I thought you changed the water pump? Tbh the fact you've got flow i'd pretty much rule out the water pump ime.
Rad, again i thought you changed this? (might be making it up now,lol)

Im beginning to wonder if you've got a crack internally somewhere and its superheating the coolant when your gunning it or of course HG. Are you losing any coolant? Done a sniff test?