Pat chuck roast dry with paper towels on cutting board. Season generously on all sides with salt, pepper, garlic powder, and dried thyme.
Heat oil in grill or cast iron skillet over high heat. Sear roast for 3-4 minutes per side using tongs until deeply browned on all sides. This step is crucial for flavor.
Transfer seared roast to slow cooker. Arrange potatoes, carrots, onion wedges, and smashed garlic around the roast.
In a mixing bowl, whisk together beef broth, red wine, tomato paste, and Worcestershire sauce. Pour over roast and vegetables.
Add bay leaves, fresh thyme sprigs, and rosemary sprigs to the slow cooker.
Cover and cook on LOW for 8 hours or HIGH for 4-5 hours, until roast is fork-tender and easily shreds.
Transfer roast and vegetables to a serving platter using tongs and a slotted spoon. Cover with foil to keep warm. Remove and discard bay leaves and herb sprigs.
Make gravy: In a small mixing bowl, mix softened butter and flour to form a paste (beurre manié). Pour cooking liquid through a fine-mesh strainer into a saucepan. Bring to a simmer over medium heat.
Whisk in butter-flour paste a little at a time, stirring constantly with whisk, until gravy thickens to desired consistency (about 5 minutes). Season with salt and pepper to taste.
Slice or shred roast on cutting board. Serve with vegetables and drizzle gravy generously over everything. Garnish with fresh parsley.