the ones that failed ended up looking like this.
amazingly it was the older style basket 04 to 05 I know your sweating it but the only two that have detonated while running has also had a turbo on it. If it aint you clutch I am thinking upgrade to the tranny or rear output bearing. the only other time I have felt a shake under load is when I burnt up two pistons and popped the head gasket. the vibration was do to the loss of compression in two cylinders.