Cook to about 170 or so and then wrap in butcher paper. It doesn’t need any more smoke and it just dries out or gets a crisp bottom. Start checking at 195-197 and check every 2-3 degrees with the probe test and it’s done when it is done. Keep it wrapped and you can even wrap it in foil but put it in a cooler with towels for at least an hour and fine for up to 5 hours before you pull and cut.

Also, make sure you are cooking a whole packers cut and that it’s adequately fatty and big enough. Smaller size and flat only much more likely to be tougher. Prime cut best.

Good luck. I freaking love brisket. Don’t worry about burnt ends while you are getting this part down. Just cut lean and fatty slices.