I've flown many, many flights on UA ex-JFK via SFO or LAX connecting to either NZ or UA international. Those UA p.s. flights have the most amazing schedule padding - even if they leave late they always seem to arrive early, often very early. It's made me much more sanguine about tight connections (though admittedly always on through tickets).

However, my similarly numerous experiences on UA ex-EWR have been much less pretty. I find that an extremely delay-prone airport. I would be faintly concerned about that connection. Honestly, I would have just called NZ to book it over the phone (the extra fee for phone booking is often offset by the fact that they have access to cheaper booking classes for the UA domestic connection, plus of course the peace of mind). On the other hand, UA seems to have similar amounts of schedule padding for their EWR-SFO/LAX flights so you may well be OK.