Yep. Longer time and cook on low setting. Something about the fibers in the meat breaking down. First they toughen up, then they break down. But when they do you'll get a very tender roast.
It is the collagen in the meat converting to gelatin that makes it pull-apart tender, from my understanding. That can be unpredictable. I've had it done at 195, and not done at 210.
The probe test is pretty good. A thermometer probe should slide into the meat almost like butter -- very little resistance.
CD