Rub the roast on all sides with the salt and pepper.
Heat the olive oil in a large pan on the stove over medium high heat. When the pan is hot, add the roast and sear on all sides until browned, about 4-5 minutes per side. Transfer roast to a clean plate.
Add the onion to the pan and cook, stirring, for 2 minutes. Add the garlic and flour to the pan and cook, stirring, for 30 seconds.
Pour in the beef broth to deglaze the pan, scraping up any browned bits. Turn off the heat and stir in the tomato paste, Worcestershire sauce and dried thyme.
Add a single layer of the carrots and potatoes to a 5 quart or larger slow cooker (the remaining veggies will fit around the roast), followed by the broth mixture from the skillet. Place the beef on top of the vegetables. Fit the remaining vegetables around the sides of the roast.
Cover and cook on low for 8-10 hours or high for 4-5 hours, until the meat shreds easily with a fork and the vegetables are tender. If you want a thicker gravy, stir in 2 tablespoons cornstarch mixed with 2 tablespoons water when there is one hour left of cooking time. Gravy will thicken best when cooked on high, so if you have been cooking the roast on low you can switch to high during the last hour.
Skim off any excess fat from the surface of the gravy and discard. Shred the beef with two forks, discarding extra fat. Season to taste with more salt and pepper, if needed. Serve pot roast with chopped fresh parsley, if desired.