That was my first brisket. I didn't have control of it the whole time and I think it was undercooked. It got a good 7 or 8 hours on it at low temp, but my sister in law was afraid it wouldn't be medium rare, so she took it off the heat when we weren't around. So, half of it was rubbery and chewy as fuck, (her half), and mine was nice and tender, but could have used another hour in the heat.
Lesson learned. Don't let you sister in law fuck with your shit.