Pat the beef chuck roast dry with paper towels and season thoroughly on all sides with kosher salt, black pepper, and garlic powder.
Heat olive oil in a large skillet over medium-high heat. Sear the beef for 3-4 minutes per side until a deep golden-brown crust develops. Transfer the roast into a 6-quart slow cooker.
Pour 1 cup of beef broth into the hot skillet, scraping up all flavorful browned bits. Pour into the slow cooker over the beef.
Add the remaining beef broth, sliced onions, minced garlic, Worcestershire sauce, balsamic vinegar, soy sauce, rosemary, and thyme sprigs.
Cover with lid and cook on LOW for 8 to 9 hours (or HIGH for 4 to 5 hours) until the beef is melt-in-your-mouth tender.
Discard herb stems. Use two forks to shred the beef directly into the juices. Let the shredded beef rest in the warm broth for 15 minutes to absorb maximum flavor.