It depends on what rear gears you have. GT's came with 3 different diffs depending on transmission and option selection.

 

My 91 5speed, stock 3.08s, is a Black / 20.


Here are the others for a 5speed
Wine / 16
White / 17
Yellow / 18
Pink / 19
Black / 20
Red / 21

Here are the ones for an Auto
Blue / 16
Green / 17
Gray / 18
Tan / 19
Orange / 20
Purple / 21

 

STOCK GEAR

THANKS THAT HELPS ALOT, MY REAR END IS STOCK AND I HAVE 5SPD TRANNY. SO IT IS DEFINITLY BLACK/20?

 

THANKS THAT HELPS ALOT, MY REAR END IS STOCK AND I HAVE 5SPD TRANNY. SO IT IS DEFINITLY BLACK/20?

If you have 3.08's, yes.

 

If there is enough of it left, you can just count the teeth and you'll have your answer.

 

what he said, and the color is well. . .the same as the one you already have. just goto the dealership.
Also fix your caps button, that is annoying when you type in all caps.