For service and parts needs, visit your dealer. You will receive genuine GM parts and GM-trained and supported service people.
Genuine GM parts have one of these marks:

California Proposition 65 WarningFuel Tank Filler Door Replacement
Fuel Tank Filler Door Replacement
Callout
Component Name
1
Fuel Tank Filler Door
Procedure
Position the fuel tank filler door to the full open position. Using light
outward sliding pressure on the filler door, ...
Exhaust Rear Muffler Heat Shield Replacement
Exhaust Rear Muffler Heat Shield Replacement
Callout
Component Name
Preliminary Procedure
Disconnect the exhaust system hangers in the rear and allow the exhaust
system to rest on the rear axle.
1
...
Special Tools (Diagnostic Tools)
Illustration
Tool Number/Description
CH-34730-2C
J-34730-2C
Injector Test Lamp
CH-38641-B
J-38641-B
Diesel Fuel Quality Tester
CH-39021-301
J-39021-301
...