here is what I found for your truck: Direct from Manual

Drive Axle Oil:

NOTE : Failure to follow the recommendation will cause shortened life due to excessive gear wear.
Select oil that meets below specifications.
API GL-5
MIL-L-2105C, D

Transmission Oil:

NOTICE
This oil is formulated for transmissions and drive trains only, and should not be used in engines. Shortened engine life will result.

NOTE : Multi-grade oils are not blended by DAE- WOO for use in transmissions. Multi-grade oils which use high molecular weight poly- mers as viscosity index improvers lose their viscosity effectiveness by permanent and temporary shear of the viscosity index improver and therefore, are not recom- mended for transmission and drive train compartments.

NOTE : Failure to follow this recommendation can cause shortened transmission life due to material incompatibility, inadequate fric- tional requirements for disk materials and/ or excessive gear wear.

The API CD/TO-2 specification or MIL-L-2104D or E oil could be used.