Don't feel so bad, I had the same results with my pastrami.
Like you, I started at 11:00 thinking I would have plenty of time as the inlaws were expected around 5:30 or so. The four pound brisket got to 168* internal temperature, but I have shoes that are more tender.
Wish I had read just a little more and understood the steaming/pressure cooking option. I will save that for the next go around with corned beef as I will look for the sales this week!
I was lucky to have put two racks of babybacks and a chicken on as well. The chicken turned out to be the best I have had in years, go figure.
UDS with Weber rotisserie, Blue Weber Performer with gas assist, Smoke Hollow elec. smoker, SJG mini-WSM, White thermapen, Blue-Backlight thermapen, Maverick ET-732 x 2, BernzOmatic JT-850 Weed Burner, BernzOmatic TS8000BZKC Hand Torch.