I totally agree on the "rubbery" thing. Yes, Grande's 50/50 is noticeably "rubbery." While I do like it, that rubbery quality does serve as somewhat of a negative factor. While some degree of rubberiness is desired, I think, in any pizza cheese, too much rubberiness -- to the point that it makes yo gaga a little when you swallow it -- is bad. Thanks for mentioning that -- I concur!
As to whether Grande 50/50 is TOO rubbery, though, I can't yet say. I still really like it. Frankly, I'd rather have some rubberiness than a noticeable lack of it -- which I think is true for the Costco grated mozzarella bags. in fact, as I write this, I am having a reheated stufed slice -- not too much rubberiness. I like the Grande 50/50.
Also, jasonmtcsn, you'll note that Costco adds "natamycin (a natural mold inhibitor)" to its product. Grande's 50/50 is just plain straight cheese -- probably why the mold. (So, on your implied suggestion, I just tossed one of my Grande 50/50 bags on the freezer!)