Transfer Case
WARNING: This page does not describe the selected car, but rather 6 other vehicles, including the 2002 GMC Sierra, 2002 GMC Cab & Chassis Sierra, 2002 GMC C3500 HD, 2002 Chevrolet Silverado, and 2002 Chevrolet Cab & Chassis Silverado. However, it is still accessible from the selected car via links, so may be relevant.
Check transfer case fluid level every 6 months or at each engine oil change. On NV246 models, change fluid every 50,000 miles. On NV261C models, periodic draining and refilling is not required.