Preheat your smoker for indirect grilling at 275 degrees F. Use hickory or oak wood for the most complementary smoke flavor.
In a small bowl, combine the salt, pepper, and garlic powder. Season your chuck roast liberally on all sides with the rub mixture. When your smoker is to temperature, place the seasoned roast on the grill and cover.
Smoke the roast until the internal temperature reaches 165 degrees F (this took 5 hours on my smoker). You should have a fairly nice dark bark on the exterior of your roast at this point. Wrap in either butcher paper or foil and return to the grill until the internal temperature is 195 degrees (this took just over an hour).
Remove the wrapped roast from the grill and allow to rest for 15-20 minutes. Cut into 3/4 inch cubes and transfer to a foil baking pan. Drizzle with most of the BBQ sauce, reserving a couple of tablespoons for later. Toss gently to coat all of the pieces in a little of the sauce.
Place the pan on the grill, close the lid and cook for an additional 1 1/2 to 2 hours, or until the sauce is bubbly and the cubed bits of beef are falling apart tender.
Sprinkle with the additional 2 Tablespoons of brown sugar and the remaining BBQ sauce. stir gently and return to the grill for just a few more minutes until everything is well incorporated. Serve hot as a main course or on white bread/buns with pickles and white onions.