2007 GMC Sierra 1500 Pickup Owner's Manual - Page 528

• The proper level for the 2500HD with the 6.6L diesel engine (RPO LLY) or 8.1L V8 engine (RPO L18), and 3500 Series is from 0.6 to 0.8 inch (17 mm to 21 mm) below the bottom of the filler plug hole. Add only enough fluid to reach the proper level. Transfer Case When to Check Lubricant It is not necessary to regularly check transfer case fluid unless you suspect there is a leak or you hear an unusual noise. A fluid loss could indicate a problem. Have it inspected and repaired. What to Use To determine what kind of lubricant to use see Recommended Fluids and Lubricants on page 629. How to Check Lubricant Four-Wheel Drive Lubricant checks in this section also apply to these vehicles. There are two additional systems that need lubrication. Manual Transfer Case 528