I have a 2004 Z71 avalanche and was trying to understand if this model has a cabin air filter to replace?
I removed the lower plastic duct, but did not see a filter housing.
No the 2004 Z71 did not come with an in cabin air filter. Some members did add one though on their own. May find some old threads in the interior mod section with info on doing it if you wish to add one.
I think this is the kit you need. You'll have to cut the factory box to add the filter. Look at Malinda's review on Amazon, it has pictures of the process