GMC SIERRA CK2 1999 Owner's Manual page 126

Camper-Type Outside Mirrors
(If Equipped)
If your vehicle is equipped with the camper
mirrors, they can be adjusted so you can have a clear
view of objects behind you.
2-48
1. To adjust the mirrors when hauling a slide
or towing a trailer, rotate the mirror by pushing the
mirror head toward the front of the vehicle.
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type
yellowblue
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in camper