We have had similar problems, just not as bad, 10th last weekend, but I have come to the conclusion that our problem and it sounds like it might be yours is the quality of the ribs to start with. As my mom always said, "you can't make a silk purse out of a sow's ear", no pun intended. If you start with poor quality ribs they will stay poor quality, and I think the quality has been declining lately for some reason.
We spritz or apply butter at 30 minute intervals. Dry may be the rub pulling the moisture out. Switch rubs for one cook and see if the dryness problem is cured.
Tough, just not cooked enough. Go ahead and overcook a slab (fall off bone) then back down cook time just a little. Fine line between fall off bone and undercooked.
Smooth Smoke BBQ Team, KCBS CBJ, 2-WSM, Cajun Bandit Conversion, wsm 2880, Smokey Joe Mini wsm, Old Country offset, several kettles.