In a large saucepan, combine the cider, vinegar, onions, oil, honey, steak sauce, and seasonings. Bring to a boil. Reduce heat; simmer, uncovered, for 20 minutes. Cool to room temperature. Remove 1 cup for basting, cover and refrigerate.
Pour remaining marinade into a large resealable plastic bag; add lamb. Seal bag and turn to coat; refrigerate for 2-3 hours or overnight, turning once or twice.
Coat grill rack with nonstick cooking spray before starting the grill. Drain and discard the marinade. Cover rib ends of lamb with foil.
Grill, covered, over medium heat for 15 minutes. Baste with reserved marinade. Grill 5-10 minutes longer or until meat reaches desired doneness (for medium-rare, am eat thermometer should read 145°F, medium, 160°F, well-done 170°F), basting occasionally.