Mix brown sugar, sweet paprika, pimentón, coriander, fennel, salt, cayenne, and cumin in a small bowl.
Sprinkle rub onto both sides of the ribs and rub into the meat with fingertips. Store excess rub in a sealed jar (will keep for several weeks).
Remove slides from Gravity Series grill. Open charcoal hopper doors. Pour in charcoal if needed and fill hopper. Light. Turn on and set temperature to 250˚F. Throw in a chunk of oak wood.
Place ribs, bone side down, on rack. Smoke for 3 hours or until browned and almost tender.
Brush ribs on both sides with cherry syrup. Continue smoking for 30 mins to 1 hour, or until ribs are tender enough to pull apart with finger. Baste ribs with cherry syrup twice during this time.
Remove from grill. Baste ribs on both sides with cherry syrup. Serve with remaining syrup on side.