Ok, so here's the finished product. I'd be lying if I said I wasn't a _little_ disappointed. I didn't expect a perfect cook but here's the thing. I don't actually know if it's under cooked or over cooked.
I saw a video from Aaron Franklin that mentioned you could tell if a brisket was over or under by how it was sliced. Thin slices hide undercooking, thick slices hide overcooking. So, as a test I sliced from under 1/4" to nearly 1/2" slices. The thinnest slices passed the "pull test", but the ticker slices were barely cutt-able with a fork. So, my initial thought was "overcooked", but the pieces near the edges of the flat seemed to be the most tender, and the center was firm, but also didn't seem dry.
So, the only really frustrating part is I don't know if it needed more or less time.
Anyway, very happy with everything else (flavor, smoke ring, grill performance, etc.)