Slow Cooker Dr Pepper Pulled Pork

Name: Slow Cooker Dr Pepper Pulled Pork
Ingredients: 3 teaspoons kosher salt , divided; 1 teaspoon ground black pepper , divided; 3 pounds boneless pork shoulder or pork butt; 2 tablespoons vegetable oil; 2 red onions , cut into slices; 1 (12-ounce) can Dr Pepper or any other cola-type soda you prefer; 1/3 cup brown sugar; 1/4 cup BBQ sauce , any favorite variety; 3 tablespoons soy sauce; 2 tablespoons honey; 1 tablespoon mustard seeds; 1/2 to 1 teaspoon chili flakes , depending on how spicy you like it; 1 1/2 teaspoons Worcestershire sauce; 1/4 teaspoon liquid smoke (optional for extra smoky flavor); 3 cloves garlic , crushed