Prepare ribs for the pressure cooker; remove the skin on the back side by slipping tip of knife between thin membrane and the bone and pulling off with a paper towel. Cut slab of ribs into sections of 3 to 4 ribs, yielding 5 sections from a slab and a half of ribs. Lightly sprinkle each side with dry rub, salt and pepper and rub seasonings into meat.
Pace rack in bottom of Instant Pot. Pour in apple juice and add liquid smoke. Scatter sage leaves and onion over the the bottom (it's okay that they fall through the rack). Place rib sections on top of rack either by layering them or placing them on their sides, it doesn't matter as long as they stay under the maximum fill line.
Seal pressure cooker and cook for 20 minutes under high pressure. When finished, let pressure release naturally for 10 - 15 minutes. While pressure is naturally releasing, preheat the grill.
If needed after 15 minutes, manually release any pressure and carefully open pot and remove ribs. Sauce ribs on both sides with BBQ sauce and finish on the grill for about 5 minutes a side. Remove to cutting board, cut into individual ribs and serve. Enjoy!