Greg
When you say "pork ribs" it's not clear if you're talking about loin backs (baby backs) or spare ribs. The former take less time to cook and cost more. Your time, 4.5 hours was probably too short for either. If they were BB, you were close; if spares, way off.
If you like the "fall off the bone" result you probably need to foil. Read the sections under cooking on the main site and you'll learn a lot. For spares, I think you'll almost certainly need 1 to 2 hours wrapped tightly (not just cover with foil) in HD foil and then finished out of the foil to get what you're looking for.
Good luck with your cooks.
Paul