Here's a really good tip I use all the time that I got on this forum regarding ribs and toothpick test.
I don't remember who it came from, but it was one of the Master Cooks that regularly contribute to the forum, was when the toothpick passes easily throught the thin end of a rack of ribs, apply sauce if you want to sauce your ribs and about a half hour later the sauce will be set and the toothpick will pass easily through the thick end of the ribs.
When I took my KCBS CBJ course we were told that ribs are only perfectly done, by KCBS standards, for about 15 minutes. Earlier then that they are underdone and after that they are over done.
Know your rib weights, keep good notes, do the toothpick test, and you'll have ribs that will amaze all who dine at your table. Heck, you'll even amaze yourslf...I amaze myself with my CS Que all the time.