First off,
(one older generation, 2 newer generation - the older one has a sticker on it like the 2Pacs did with it's serial on it, the 2 newer ones don't and the chips are tan colored instead of black like my original NewPac)
Even as the manufacturer, I have no idea what this means.
Second, Windows 10 sucks. Don't use it. I mean not just for mining, but like for anything. Ever. In addition to just being terrible in general, it also does some weird stuff to USB packets that has caused issues with R606 hashrate and stability. Might be bumping into some of the same issues.
Third, have you adjusted voltages at all? I'm assuming you have at least on the 2Pacs in order to get the hashrate you have, since that's way above stock speed. NewPacs with top-shelf chips can run 600MHz at stock voltage but I only guarantee stock speed on every stick; getting more than that will require tuning. It's also entirely possible one stick is inferior. The chips we get are kind of a grab-bag for quality.