Cut four slits (taking care to cut with the grain of the meat) in the beef roast. Cut bacon into 4 pieces, each about the width of a middle finger and as long as the slits. Dredge bacon pieces in cayenne pepper and garlic powder to coat on both sides; insert the seasoned bacon into the slits in the roast.
In a saucepan over medium heat, melt the butter. Add flour and cook, stirring, for 2 minutes to make a roux. Very gradually add the beef stock and bring to a boil, continuing to stir until sauce has thickened. Fold in the carrots, garlic, and pickle.
Place beef roast in slow cooker and pour the gravy over it. Cover with lid and cook on Low for 7.5 hours, then remove roast; slice meat and return to gravy to cook for 30 more minutes.