Sorry to hear about your ribs. What type of cooker were you using and what were you using to gauge the temp of the unit - the built in thermometer or electric thermometer? Let us know and we can try to figure out went wrong.
My initial thought is that you over-cooked the ribs. With BB ribs, I cook at 250 for about 3 hours and they are done. I think the last 2 hours you did at 350 killed it, but I'm interested in what your equipment was.
Traeger 070 & Jr., Mini WSM, UDS, Akorn, Weber gasser, BGE(sold)