[desertrat]

Yes it is an open diff.

I'm not sure if our trucks w/ Eatons every came factory w/ posi.
Also in my opinion posi-traction is not a locker. Someone might correct me but a true locker will not slip and a posi-traction still slips.
As far as I know there has never been a factory vehicle with a locker rear end, since a locker is not always safe to drive on the streets (but it sure is fun).