Chevrolet 2003 Silverado Owner's Manual page 513

100,000 Miles (166 000 km)
Inspect spark plug wires. An Emission Control
Service.
Replace spark plugs. An Emission Control Service.
Change automatic transmission fluid and filter if
the vehicle's GVWR is over 8600 lbs, if the
vehicle has an Allison transmission or 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.
− Uses such as found in taxi, police or delivery
service.
If you haven't used your vehicle under severe service
conditions listed previously and, therefore, haven't
changed your automatic transmission fluid, change
both the fluid and filter
Automatic Transfer Case Only: Change transfer case
fluid
Except 8.1L V8 Engine: Inspect Positive Crankcase
Ventilation (PCV) valve. An Emission Control
Service.
150,000 Miles (240 000 km)
Drain, flush and refill cooling system (or every
60 months since last service, whichever occurs first).
See Engine Coolant on page 5-30 for what to use.
Inspect hoses. Clean radiator, condenser, pressure
cap and neck. Pressure test the cooling system
and pressure cap. An Emission Control Service.
Change five-speed manual transmission fluid (with
4300 V6 or 4800 V8 engines only).
Inspect engine accessory drive belt. An Emission
Control Service.
200,000 Miles (332 000 km)
6000 V8 Engine Only: Change five-speed manual
transmission fluid.
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