You could also try adding some Redline water wetter to your coolant. I've heard some good things about this product although I haven't personally used it myself because my car runs cool. I have, however put a bottle of this into my project car(that's not quite running yet) along with a new Nissans 3 row radiator like you did so we'll se what happens. If you're interested in trying this you can get some at most auto parts stores like Autozone, Napa, etc. Good Luck!