GMC 1999 Sierra 1500 Pickup Owner's Manual page 290

Service & Appearance Cave
PO503
3. The filter is behind the air cleaner on the intake manifold. Unscrew and
take off the ring nut from the the top
of the filter head. Lift the element
out of the filter head.
4. If there is any dirt on the element sealing surface
of the filter head,
clean it off.
...
t
PO212
5. Line up the widest key slot in the top of the new element with the
widest key on the filter head and push the element in until the mating
surfaces touch.
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