GMC Sierra Owner's Manual page 396

Service and Maintenance 395
Maintenance Schedule Additional
Required Services - Severe
Rotate tires and perform Required Services. Check engine oil
level and oil life percentage. Change engine oil and filter,
if needed.
Check engine air filter life percentage and status. Change
engine air filter, if needed. (1)
Replace passenger compartment air filter. (2)
Inspect evaporative control system. (3)
Replace spark plugs. Inspect spark plug wires and/or boots.
Change automatic transmission fluid and filter.
Change transfer case fluid, if equipped with 4WD. (4)
Drain and fill engine cooling system. (5)
Visually inspect accessory drive belts. (6)
Replace brake fluid. (7)
Replace windshield wiper blades. (8)
Replace hood gas struts and tailgate dampener. (9)
Replace air conditioning desiccant. (10)