First, let me say that cooked ribs should not be falling off the bone tender. In the barbecue world, those are called "restaurant ribs" and are considered to be overcooked. I know this because I'm a certified Memphis barbecue judge . For correctly cooked ribs, the meat should still be attached to the bone but should come away when tugged on. In addition, the meat should still have a little "chew" to it. Second, even though pork is technically done at 145 degrees, ribs require a bit higher temperature in order for the collagen to break down into gelatin for the most desirable bite. That happens at about 165 degrees.  Having said all that, however, if you like your ribs falling off the bone, then that's the way you should cook them! In that case, take them up to between 195 and 205 degrees.