2001 GMC Sierra 1500 Pickup Owner's Manual - Page 367

Automatic Transmission Fluid (AllisonR Only) When to Check and Change A good time to check your automatic transmission fluid level is when the engine oil is changed. Change both the fluid and filter every 25,000 miles (41 500 km) if the vehicle is mainly driven under one or more of these conditions: How to Check Because this operation can be a little difficult, you may choose to have this done at the dealership service department. If you do it yourself, be sure to follow all the instructions here, or you could get a false reading on the dipstick. NOTICE: Too much or too little fluid can damage your transmission. Too much can mean that some of the fluid could come out and fall on hot engine parts or exhaust system parts, starting a fire. Be sure to get an accurate reading if you check your transmission fluid. Wait at least 30 minutes before checking the transmission fluid level if you have been driving: D In heavy city traffic where the outside temperature regularly reaches 90_F (32_C) or higher. D In hilly or mountainous terrain. D When doing frequent trailer towing. D 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). See "Scheduled Maintenance Services" in the Index. D D D D When outside temperatures are above 90_F (32_C). At high speed for quite a while. In heavy traffic -- especially in hot weather. While pulling a trailer. 6-25