1997 GMC Sonoma Owner's Manual - Page 354

I LongTripmighwayMaintenanceSchedule I 50,000 Miles (83 000 km) 17 Change automatic transmission fluid and filter if the vehicle is mainly drivenunder one or more of these conditions: - In heavy city traffic where the outside temperature regularly reaches90 O 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. IJ'you do not use your vehicle under any of these conditions, thefluid andfilter do not require changing. Manual transmission fluid doesn't require change. DATE ACTUAL MILEAGE SERVICED BY. 7-44