GMC 2003 C4C042 Owner's Manual page 239

Single Drive Rear Axle
Disconnect the propshaft at the rear axle. Secure the
propshaft to the frame or crossmember.
Tandem Drive Rear Axles
(Forward Axle Off the Ground)
Raise the front of the vehicle until the forward tandem
axle wheels are off the ground. Remove the rearward
propshaft.
5-14
Tandem Drive Rear Axle (Both Axles on the Ground
Due to Type of Suspension or Attached Load)
Disconnect the propshaft at the forward tandem axle.
Secure the propshaft to the frame or crossmember.
If there is damage or suspected damage to the axle(s),
remove all axle shafts. Cover the hub openings to
prevent the loss of lubricant or entry of dirt or
foreign objects.
After Towing
1. Block the rear wheels and install axle and propshafts.
2. Check for proper phasing of universal joints.
3. Apply the emergency brake system before
disconnecting from the towing vehicle.