[Raven87]

From the manual:

Usage Fluid/Lubricant
Rear Axle (L4 and V6 Engine with Automatic Transmission)
Dexron non-LSD Gear Oil (GM Part No. 88863089, in Canada 88863090).

Rear Axle (L4 and V6 Engine with Manual Transmission)
Rear Differential Fluid 75W-90 Limited Slip (GM Part No. 88900401 and
Limited Slip Additive 88900330, in Canada 89021678 and Limited Slip
Additive 00992694).

Rear Axle (V8 Engine)
Rear Differential Fluid 75W-90 Limited Slip (GM Part No. 88900401, in
Canada 89021678).
Add Limited Slip Additive GM Part No. 88900330, in Canada 00992694