Okay, I just looked up "block" mozzarella. I haven't seen them before. Not here or NE. Anyhow, this article seems decent on what kind of cheese to look for, thoroughly disses the shredded as having cornstarch or other coatings and improper melting. I thought there was something funky about the shredded. Now I know why. Anyhow, it does recommend blocks of whole milk and brand not as big a factor. Teaches what to look for when it melts to determine best one.
http://slice.seriouseats.com/archive...or-pizzas.html