Trim the brisket, leaving about 1/4 inch of fat cap. Coat with a thin layer of mustard.
Mix the pepper, salt, and garlic powder and apply an even, heavy rub.
Preheat the pellet grill to 225°F and place the brisket fat-side up.
Smoke until the bark is set and the internal temperature reaches 165°F (6-8 hours).
Wrap tightly in butcher paper and continue until it probes tender at 203°F (3-4 more hours).
Rest, wrapped, in a cooler for at least 1 hour.
Slice against the grain, separating the flat from the point.