1996 GMC Sonoma Owner's Manual - Page 238

Automatic Transmission Fluid When to Check and Change A good time to check your automatic transmission fluid level is when the engine oil is changed. If you do it yourself, be sure to follow all the instructions here, or you could get a false reading on the dipstick. I C E : Too much or too little fluid can damage your transmission. Too much can mean that some of out the fluid could come 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: When outside temperatures are above 90°F (32°C). 0 Change both the fluid and filter every 50,000 miles (83 000 km) 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. 0 Uses such as found in taxi, police or delivery service. If you do not use your vehicle under any of these conditions, the fluid and filter do not require changing. See "Scheduled Maintenance Services" in the Index. At high speed for quite a while. In heavy traffic -- especially in hot weather. 0 How to Check Because this operation can be a little difficult, YOLImay choose to have this done at your GM dealer's Service Department. While pulling a trailer. To get the right reading, the fluid should be at normal operating temperature, which is 180°F to 200°F (82°C to 93°C). 6-16