Combine hot sauce, molasses, vinegar, and ¼ cup mustard. Pour into a spray bottle and set aside.
Coat brisket with ½ cup of the mustard. Set aside.
Combine seasonings and salt. Press mixture into both sides of brisket. Refrigerate overnight.
The next day, heat up a smoker to 200°F with the mesquite chunks. Add brisket and cook 9 hours, spraying every 3 hours with vinegar mixture, and changing wood as needed to keep temperature at 200°F.
Remove brisket from smoker and let rest ½ hour. Separate along the fat line and slice thinly across the grain.
Finely chop slices and toss with remaining vinegar mixture. Place 1/9 into each bun and serve warm.
If you don't have a smoker, just preheat your oven to 190°F. Place ¾ cup soaked mesquite chips in the bottom of a roasting pan and add a rack and your rubbed brisket. Cover tightly with foil and cook the same.