To prepare the rub: Combine all rub ingredients in a bowl and stir to mix.
Preheat a grill or the oven to 250 degrees F.
Place slab of ribs bone side up on table. Slide a knife under the membrane and against the end bone to separate the two. With a dry paper towel or rag, grasp the edge of the thin membrane and pull. The entire membrane should separate from rib. Note: This will result in a more tender rib and will allow your barbecue flavors to better penetrate the meat.
Sprinkle 1/4 cup of rub over each slab, front and back. Place ribs, meat side up, on the grill or in the oven for 2 hours. Remove and place each slab on a doubled aluminum foil square, meat side down. Pour 1 cup apple juice over each slab while wrapping tightly in foil. Cook for 1 more hour at 250 degrees F. Remove slabs from foil and sprinkle with another 1/4 cup of rub. Cook an additional 1 hour, uncovered, until ribs are tender.
In the meantime, mix together the barbecue sauce ingredients in a saucepan. Stir to mix and bring to a simmer and cook 10-15 minutes. Let sauce cool.
To finish: Remove ribs from the grill or oven, paint with finishing glaze and cook for another 15 minutes. Cut and serve with additonal sauce.