Where have they been?
On offense, they've been dealing with significant personnel issues from the get go - only three WRs available for the first three games, subsequent injury issues ... especially Gronk, Michel, Burkhead, not to mention losing Hill after a handful of snaps.
On defense, the emergence of JC Jackson since the BYE has helped immensely, but they were quietly getting better, incrementally, even before that, especially with regard to communicating with each other.
Basically, everybody got healthy and everything else has finally come together. It just took a little longer than usual this season.