Spray the bottom of a 4.5 quart (or bigger) slow cooker with vegetable oil.
Wash, dry, and remove the skin from ribs and transfer to slow cooker folding the ribs gently. You can also cut the ribs so it will be easier to take them out later. (see notes) Season generously with salt and pepper.
In a large bowl combine barbecue sauce, brown sugar, garlic, cayenne. Pour half of the sauce over the ribs in the slow cooker. Reserve the remaining sauce for later to brush the ribs.
Cook on HIGH for 3 hours or LOW for 7 hours until fork-tender. (See notes)
When cooked, carefully transfer to a baking sheet lined with parchment paper or foil. Pour the juices from the slow cooker into the bowl with barbecue sauce. Stir to combine and baste the ribs generously with the sauce (you may not need to use the whole sauce, reserve for later). Broil in the oven for 10 minutes at 425 Fahrenheit until charred and crisp on the outside.
Serve with remaining sauce.