GMC 1997 Safari Owner's Manual page 330

Maintenance Schedule
Follow this maintenance schedule only if none of
the conditions from the Short Trip/City Maintenance
Schedule is true. Do not use this schedule if the vehicle
is used for trailer towing, driven in a dusty area or used
off paved roads. Use the Short Trip/City schedule for
these conditions.
Driving a vehicle with a fully warmed engine under
highway conditions causes engine oil to break
down slower:
Every 7,500 Miles (12 500 km): Engine Oil and Filter
Change (or every 12 months, whichever occurs first).
Chassis Lubrication (or every 12 months, whichever
occurs first). Drive Axle Service. Tire Rotation.
Transmission Service (severe conditions only).
Every 15,000 Miles (25 000 km): Automatic
Every 30,000 Miles (50 000 km): Fuel Filter
Replacement. Air Cleaner Filter Replacement. Front
Wheel Bearing Repack (2WD only) (or at each brake
relining, whichever occurs first). Automatic
Transmission Service (normal conditions).
Drive Belt Inspection. Fuel Tank, Cap and Lines Inspec
Inspection. Spark Plug Replacement. Positive
Crankcase Ventilation (PCV) Valve Inspection.
Service (or every 60 months, whichever occurs first).
Every 60,000 Miles (100 000 km): Engine Accessory
Every 100,000 Miles (166 000 km): Spark Plug Wire
Every 150,000 Miles (240 000 km): Cooling System
These intervals only summarize maintenance services.
Be sure to follow the complete maintenance schedule
on the following pages.