Make the rub: Combine the smoked paprika, sweet paprika, salt, brown sugar, dry mustard, black pepper, garlic powder and onion powder in a small bowl. Mix well.
Preheat the oven to 325°F, line 2 shallow baking pans with heavy duty aluminum foil and coat them with nonstick spray.
Sprinkle about 2/3 of the rub mixture over the meaty side of the ribs and rub into the meat with your fingertips. Turn the ribs over and repeat with the remaining rub.
Arrange the ribs on the prepared pans and cover tightly with foil. Bake until tender, 1-1/2 to 2-1/2 hours, depending on the thickness of the meat. When the ribs are done, juices should run clear and the meat will pull away from the bone easily with a fork.
Prepare the sauce: Combine the Jack Daniel's, ketchup, brown sugar, molasses, Worcestershire sauce, vinegar, garlic and mustard in a small saucepan and bring to a boil. Reduce the heat to medium and simmer, stirring frequently, until the sauce has thickened to the consistency of ketchup, 8 to 10 minutes. Set aside until ready to serve.
Grill the ribs: Preheat a gas or charcoal grill to medium heat (375 to 400°F) and oil the grates. Brush the ribs with the barbecue sauce and place them on the grill. Cook until nicely browned, turning the racks over frequently and brushing with sauce each time, 8 to 10 minutes total.
You may want to cut the racks in half prior to grilling to make turning them easier - long racks can be somewhat unwieldy. For easy cleanup, you can also grill the ribs on oiled, heavy-duty aluminum foil. They will still brown nicely; just increase the cooking time by a minute or two.
To serve, cut the racks between the bones to make individual ribs and pass the remaining barbecue sauce at the table.