Season the chuck roast thoroughly with salt and pepper on all sides.
Heat olive oil in a large skillet and sear the roast over medium-high heat until browned on all sides, about 3-4 minutes per side.
Arrange onion wedges, carrots, and quartered potatoes in the bottom of the slow cooker.
Place the seared roast on top of the vegetables and scatter the peeled garlic cloves around and on top of the meat.
Lay the fresh rosemary and thyme sprigs over the roast.
Whisk together beef broth, balsamic vinegar, and Dijon mustard, then pour the mixture into the slow cooker.
Cover and cook on low for 8 hours or until the meat is fall-apart tender and the garlic is soft and caramelized.
Remove herb stems, slice or shred the roast, and serve with the vegetables and garlic, drizzling the cooking juices over everything.