In a small bowl, mix together the garlic, thyme, rosemary, salt, pepper and olive oil. Spread this mixture evenly all over the 2 chuck roast.
In a 6 quart slow cooker, using a wooden spoon, mix together the tomato sauce and red wine. Scatter the onion, fennel and potatoes around the bottom of the pan. Nestle the 2 pieces of chuck into the vegetables and cook on low for 8 hours.
Remove the pot roast from the slow cooker and cover with foil to keep warm. Using a small ladle, skim off any fat that may be on top of the juices left in the pan and discard. Slice the pot roast and serve along side the braised fennel and potatoes. Spoon some of the remaining juices over the roast before serving.