Rear end gears on 90 GT?

[ultrastang]

There should be an I.D. tag affixed to one of the rear end's rear cover bolts. There will be two strings of letters and numbers on the tag. Starting with the second string, should read something like: 2.73, 2L73, 3.08, 3L08, etc. This will be the rear end ratio. The "L" denotes a locking differential (Tracion-Lok). An even easier way to tell, without crawling under the car, is to look at the warranty sticker, on the driver's side door jamb, under the "Axle" heading.
In 1990:
2.73:1 is code letter M (locking) or code number 8 (non-locking).
3.08:1 is code letter Z (locking) or code letter Y (non-locking).
3.27:1 is E (locking) or 5 (non-locking).
3.45:1 is R (locking) or F (non-locking).
3.73:1 is W (locking_ or 6 (non-locking).