I always detele the Cache after I change something in Cloth. That's Maya Cache 101
It just doesn't simulate the way it's supposed to. I think it's just too much to simulate. I edited my scene, took away the model and the t-shirt and all, and just had those suspendors, then I simulated that, then it worked properly with the constraints. Except the verticies were flying everywhere. And I think that's just because it needed to be stiff... But I dunno.
I've been trying to find some other way to animate it so it looks like cloth but... Nothing's coming to mind.