2003 GMC Sierra 1500 Pickup Owner's Manual - Page 506

25,000 Miles (41 500 km) CI Allison Transmission Only: Change automatic transmission fluid and filters if the vehicle is mainly driven under one or more of these conditions: In heavy city traffic where the outside temperature regularly reaches 90°F (32°C) or higher. - In hilly or mountainous terrain. - 37,500 Miles (62 500 km) U Check readfront axle fluid level and add fluid as needed. Check constant velocity joints and axle seals for leaking. iII Rotate tires. See Tire Inspection and Rotation on page 5-74 for proper rotation pattern and additional information. (See footnote +.) 45,000 Miles (75 000 km) U Inspect engine air cleaner filter if you are driving in dusty conditions. Replace filter if necessary. An Emission Control Service. (See footnote t.) U Check readfront axle fluid level and add fluid as needed. Check constant velocity joints and axle seals for leaking. 0 Rotate tires. See Tire Inspection and Rotation on page 5-74 for proper rotation pattern and additional information. (See footnote +.) - When doing frequent trailer towing. - Uses such as found in taxi, police or delivery service. If you don't use your vehicle underany of these conditions, change the fluid and filter every 50,000 miles(83 000 km). 30,000 Miles (50000 km) U Check readfront axle fluid level and add fluid as needed. Check constant velocity joints and axle seals for leaking. 0 Rotate tires. See Tire Inspection and Rotation on page 5-74 for proper rotation pattern and additional information. (See footnote +.) L I Replace fuel filter. An Emission Control Service. (See footnote t.) 0 Replace engine air cleaner filter. An Emission Control Service. 6-7