1998 GMC Jimmy Owner's Manual - Page 284

Automatic TransmissionFluid When to Check and Change Operating the engine withthe air cleaner off can cause you or others tobe burned. Theair cleaner not only cleans the air, it stops flame if the engine backfires. If it isn't there, andthe engine backfires, you could be burned. Don't drive with it off, and be careful working on the engine with the air cleaner off. L A good time to check your automatic transmission fluid level is when the engine oil changed. is Change both the fluid and filter every 15,000 miles (25 000 km) if the vehicle ismainly driven under one or more of these conditions: In heavy city traffic where the outside temperature regularly reaches 90O F (32 C) or higher. O In hilly or mountainous terrain. When doing frequent trailer towing. NOTICE: I the air cleaner is off, a backfire can cause a f damaging engine fire. And, dirt can easily get into yourengine, which will damage it. Always have the air cleaner in place when you'redriving. 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 filter every and 50,000 miles (83 000 km). See "Scheduled Maintenance Services"in the Index. 6-15