Im going to take a HUGE chance and run the same thing in both axles.....
What mentally deficient group of designers at GM thought it would be cool to make them that close, BUT different!? Unbelievable.
Front Axle – Four-Wheel Drive SAE 75W-90 Synthetic Axle Lubricant (GM Part No. 88900401, in Canada 89021678).
Rear Axle (1500 Series) SAE 75W-85 Synthetic Axle Lubricant (GM Part No. 19300457, in Canada 19300458).