Place the chuck roast into the base of the slow cooker.
In a small bowl, combine the Kosher salt, cracked black pepper, onion powder, and Italian seasoning. Mix thoroughly and rub this seasoning blend generously over the roast.
In a separate medium-sized bowl, whisk together the balsamic vinegar, brown sugar, Worcestershire sauce, beef broth, and minced garlic.
Pour the prepared balsamic sauce over the roast in the slow cooker, ensuring it is evenly distributed.
Cover the slow cooker and cook the roast on the low heat setting for 8-10 hours, until the beef is fork-tender.
After cooking, in a small bowl, combine the cornstarch and water to form a slurry. Stir this mixture into the liquid in the slow cooker, allowing it to thicken the sauce.
Continue cooking for an additional 30-60 minutes until the sauce reaches the desired consistency.
Shred the cooked beef using two forks, then serve it over mashed potatoes for a complete meal.