Only those with traction control use the open diff. The 5sp cars HAVE traction lock. I am not sure wether or not 5sp cars had traction control or not, but I do know that the cars that don't have traction control have traction lock. The reason, as far as I know, that they use an open diff in the trac control is that the rear brakes are used as part of the traction control function.
Jeff
Yes 3.31's in the auto. I have a set here pulled from a 94' auto.