Low air volume or velocity coming from my vents?

I’ve been chasing down an issue with low air volume or velocity coming from my vents.

2009 T660

Today, I removed the glove box and lower panel to find that I have air escaping behind the heater box. Does anyone have a reference to a video or schematic that shows how things look behind there where I can’t see? I hate to break air conditioning lines to remove the components in the engine bay without knowing what I may be facing. I’m still working the truck and having a/c in 100+ degree temperatures is necessary.

When I feel around the back, I can feel a rubber flap. While the fan is running, it’s open. And when the fan is turned off, the flap relaxes. I have a feeling that maybe something is missing or misaligned because I don’t think I should be able to feel this rubber flap where air is supposed to be contained and directed to the vents.

Any help will be greatly appreciated.