Preheat oven to 350 degrees F (175 degrees C). Place roast in a 9x13 inch pan, sprinkle with garlic salt, and cover with foil.
Bake in preheated oven for 3 to 4 hours, or until a meat thermometer inserted reads 145 degrees F (63 degrees C). Preheat an outdoor grill for high heat and lightly oil grate.
Grill roast for 10 minutes on each side. Return roast to the pan, and shred the meat using two forks. Stir in barbecue sauce, and return to the oven for 20 minutes, or until heated through. Spoon meat onto buns.