1999 GMC Sonoma Owner's Manual - Page 340

yellowblue Long Trip/Highway Scheduled Maintenance 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. - When doing frequent trailer towing. - Uses such as found in taxi, police or delivery service. If you do not use your vehicle under any of these conditions, change the fluid and filter every 50,000 miles (83 000 km). j Rotate tires. See "Tire Inspection and Rotation" in the Index for proper rotation pattern and additional information. (See footnote +.) j Replace fuel filter. An Emission Control Service. (See footnote[.) j Replace air cleaner filter. An Emission Control Service. j Change engine oil and filter (or every 12 months, whichever occurs first). An Emission Control Service. j Lubricate chassis components (or every 12 months, whichever occurs first). (See footnote #.) j Check rear/front axle fluid level and add fluid as needed. Check constant velocity joints and axle seals for leaking. (See footnote **.) j For Two-Wheel-Drive vehicles only: Clean and repack the front wheel bearings (or at each brake relining, whichever occurs first). j Change automatic transmission fluid and filter if the vehicle is mainly driven 30,000 Miles (50 000 km) DATE ACTUAL MILEAGE SERVICED BY: 7-32