HVAC Restricted Flow

The air flow in my '97 XJ's HVAC system seems to be restricted. Barely any air comes out of the vents no matter what the fan speed(when I increase the fan speed the flow from the vents dosn't increase). Heat or cold it flows the same. It does divert the air to the proper vents. I pulled the blower motor to check for a blockage and didn't find any. Any ideas before I pull the whole dash apart to look in the air box?

Seems to me there is a known problem with the 97+ airbox, something breaks frequently inside.

Not a recommendation, but some decent info here: http://www.heatertreater.net/jeep Cherokee 97-04.html

But would a blend door failure cause restricted flow?

My roommate's 2000 had this same issue. Its a royal pain to fix, but it's also a royal nuisance to anyone who has been in one of these. Basically, part of the foam seal falls into the fan box and jams up the works. Makes a lot of noise and air seems to come out of all the vents but not as much air as it sounds like you should be getting. You have to disconnect the A/C lines going into the firewall to pull the fan motor on these from what I remember. Once you disconnect the line, it will allow the accumulator/dryer to swing up and out of the way to allow you to access the air box. Then button up and refill the freon.

Any other input before I pull the while dash apart? Could a blend door problem cause significantly restricted flow?