Hi 71! Glad to have you with us!
Sounds like you've spent some time here, and looks like you had a great plan going. Doesn't look, to me, like you did anything "wrong." What I think happened - the one thing you didn't ask about - was your meat. The quality of the meat tends to be the biggest factor, especially for ribs. Personally, I only buy ribs (backs or spares) from Sam's Club. Their 3-packs are outstanding quality, and always yield great results (moist, tender).
Last time I bought a couple of racks from a grocery store, I had exactly the same results as you did, which was way off "normal" for my ribs! That's when I decided that where you buy meat is a huge factor in outcome.
I would suggest trying a different vendor - Sam's, if you have one near, before you go and revamp your whole approach (which looks good to me).
Just a side note - now that you're here, how about adding a first name and town to your signature line? We're pretty familiar, around here, and like to know who our new friends are!