So I have the solution for tough ribs.
Cook them longer.
Due to a fried 150AMP three-phase breaker in my office, they got cooked a lot longer than I wanted.
I was doing my cold-smoked brasied ribs with baby backs.
I figure they got 5 hours @ 275F..
The ribs were great and they fell apart.
I hear lots of recipes for "great" ribs in 3-4 hours, but, I can't do it.
I like 'em @ 225 for 8hrs.
(always works for me).