1999 Chevrolet Silverado 1500 Pickup Owner's Manual - Page 392

yellowblue Scheduled Maintenance -- Gasoline Engines 100,000 Miles (166 000 km) (Continued) Change automatic transmission fluid and filter 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. - When doing frequent trailer towing. - Uses such as found in taxi, police or delivery service. j If you haven't used your vehicle under severe service conditions listed previously and, therefore, haven't changed your automatic transmission fluid, change both the fluid and filter. j Inspect Positive Crankcase Ventilation (PCV) valve. An Emission Control Service. j 7-16