Air flow/Cabin Filter

[Nanniepoo]

The other day while driving, I'm sweaty and hot but my wife was freezing. She eventually pointed her vent at me and I realized the air flow from the passenger vents, all of them, was significantly higher than the driver's side. I played around with the vent settings which didn't really help, and considering the same thing happens when it's on max AC and full flow, I think there's a problem somewhere. I'm going to start with replacing the filters but wanted to check in here to see if others have ran into similar problems. Really hoping there's not a stuck flap in there or something.

And on the topic of filters, what's the difference between activated charcoal and non? Are they interchangeable? Activated charcoal seems like it would be better, but it's actually cheaper on BavAuto...

This is on an '08 4.8 with 4 zone.

Thanks!