I think your problem is that your dough is too dry. Flour is tricky stuff (especially high-gluten flour which needs more hydration)--its water absorption rates vary depending on when and where it was grown, how old it is, the altitude where it is used, the humidity, etc., etc. This is why I object to using a scale--flour is not precisely scientific.
I knead my dough by hand, by feel--so I know when it needs more water. Your final dough ball should be plaible, smooth, shiny--some pizza makers prefer a dough that's a little too wet.