I still havn't looked under my hood lol. But I'm gonna today, or maybe tomorrow.

 

My 01 2500 hd crew cab has 2 cabin air filters located under the passenger side dash in the black heater core housing YouTube how to change cabin air filter silverado there are plenty of videos for your year and above that's how I learned where mine was there not that hard to replace either or that expensive for that matter took me 10 minutes to do it

 

Great idea NullHead
Here ya go