If I were there, the diff would be the first thing I would point to.
If you really look back at most all stock dif failures - not the point that something happened, but the point the gears finally snap in half - you will find that this happens during a turn. It makes sence because the dif does most of it's work during a turn. There's also tons of stories out there about someone running their car hard or just having some fun one day, then a week or so later they are leaving a stop sign or red light, make a turn and BOOM!!
What has probably happened is a sun gear cracked at some point. When, where or how it cracked? Your guess is as good as mine, but if I had to put money on it, I would have to say that it was at the same time your tranny mount broke or soon after. Then today the gear finally started coming apart on you.
Sorry to hear about it and hope you can get her back up and running again.
