Make the brisket: Preheat the oven to 350°F
Place the brisket in a roasting pan. In a small bowl, combine 3 tablespoons of salt and the black pepper, then sprinkle evenly across the entire brisket, making sure to cover the edges as well.
Roast the brisket until a crust begins to form, about 1 hour. Reduce the oven temperature to 300°F. Cover the brisket with foil and continue roasting until the internal temperature reaches 190°F on a meat thermometer, about 2 hours. Remove the brisket from the oven and let rest for 20 minutes. Keep the oven on.
Transfer the brisket to a cutting board and dice into 1-inch pieces. Return the brisket cubes to the pan.
Make the sauce: In a small saucepan over medium-high heat, boil the cola until reduced by half, about 5 minutes. Add the barbecue sauce, brown sugar, Worcestershire sauce, and soy sauce. Stir to combine, then bring to a boil.
Pour the sauce over the brisket cubes and toss to coat. Place the roasting pan, uncovered, into the oven and continue cooking until the sauce becomes thick and syrupy, about 1 hour.