What kind of gear oil does my 2006 Chevy Silverado need?

[Viperdude5064410]

I have a 2006 Chevrolet Silverado 1500 Z71 (4x4) and I need to know what kind (SAE grade) of oil does my differential require?

For the record I have modified the truck quite a bit and I now have 627 rwhp so if that makes a difference in what gear oil I should use please do tell.

 

[bandit_60]

80/90 gear oil. you can get it at auto zone with the limited slip additive in it.