What year did TOR$EN start in US cars?

["Lewis, Gary M" <Gary.Lewis@West.Boeing.com>]

Hi folks,
What year did the TORSEN diff start?  I thought it was 1991, I was just told
that it was 1989.  If it was 1989, was it ALL 1989 or just the MAC-14 (late)
1989.  I need to know in the next hour if possible.
thanks,
Gary