For the front :
1. Raise the vehicle.
2. Make sure the vehicle is level.
3. Inspect the front axle for leaks. Repair as
4. Remove the front differential carrier shield, if equipped.
5. Clean the area around the front axle fill plug.
6. Remove the front axle fill plug (1).
7. Inspect the oil level. Specification
o For the 8.25 inch axle, the oil level should be between 12-16 mm (0.50-0.625 inch) below the fill plug opening.
o For the 9.25 inch axle, the oil level should be between 6-10 mm (0.25-0.375 inch) below the fill plug opening.
8. If the level is low, add oil until the level is between 12-16 mm (0.50-0.625 inch) for the 8.25 inch axle or 6-10 mm (0.25-0.375 inch) for the 9.25 inch axle. Use the proper fluid. Refer to Fluid and Lubricant
9. Install the fill plug.
o Tighten the plug to 33 Nm (24 ft. lbs.) .
10. Install the front differential carrier shield, if equipped.
11. Lower the vehicle.
I dont know what transfer case you have IF YOU know the model type i can look up the other two model options.
Transfer Case - BW 4481-NR3
Transfer Case Fluid Replacement
Removal Procedure
Important: When performing the following procedure, use only hand tools to remove and install the drain and fill plugs.
1. Raise and suitably support the vehicle.
2.Remove the transfer case shield, if equipped.
3. Remove the fill plug.
4. Remove the drain plug. Important: Ensure that an approved drain pan is used when draining the transfer case.
5. Allow the transfer case to drain completely.
Important: Use only drain and fill plugs that are made from aluminum. Steel or brass plugs are not compatible with the magnesium case.
1. Apply sealant GM P/N 12346004, (Canadian P/N 10953480), or equivalent, to the threads of the drain and fill plugs.
2. Install the drain plug.
o Tighten the plug to 25 Nm (18 ft. lbs.) .
3. Fill the transfer case to the bottom of the fill plug hole with DEXRON(R) III, GM P/N 12346143, (Canadian P/N 10952622).
4. Install the fill plug.
o Tighten the plug to 25 Nm (18 ft. lbs.) .
5. Install the transfer case shield, if equipped.
6. Lower the vehicle.