Season flour with salt and pepper. Dredge the meat in flour. Heat 2 tablespoons olive oil in a skillet. Shake excess flour off the meat and brown it in two batches. Place browned meat in crock pot. Add remaining oil to the heated skillet and cook carrots, celery, onion & potatoes for 10 minutes, stirring occasionally. Place sautéed vegetables in crock pot on top of meat. Pour stock and tomato paste into skillet and stir to deglaze the pan and pour mixture over meat and vegetables in the crock pot. Add thyme, cover and cook on the high setting for 2 hours. Taste the broth and adjust salt and pepper to taste. Drop the temperature to the low setting and continue cooking for an additional 3-4 hours, or until meat is fork tender. You can also just do the entire cooking process on low for 6-8 hours (for those who just want to get it going in the morning and leave it for the day) and adjust the seasoning at the end.