cold air coming in

I have a 2001 HD 2400 which has been a great truck, but lately there sometimes is cold outside air coming from under the dash on the passenger side. I've reached up there and couldn't feel anything out of place but couldn't really tell much. I had to tape trashbags under there to keep my wifes feet from freezing. I tried all positions on the controls with no change. Any ideas?

not sure, but this winter I had the same ting happening to me but it was coming through the center consoul. right where the cup holders are. weird.

I seen a thread in the Tahoe forum on the same problem, check there. It has been 2-4 weeks ago.