Just traded the PSD for an 02 Dmax, the wife tells me that she feels a cold breeze from under the dash on the passenger side. It only seems to happen when the fan motor is on 1, if I turn it up to 2 or above, draft goes away. Its like my old Ford with the slide vent on the kick panel. The draft doesn't bother me except when the wife is riding shot gun and that means it NEEDS to be fixed ):h
Anyways, anything I should know before I crawl under the dash?

I found the long bed doesnt do that....imho....

There was a service bulletin on this. If I remember right it has something to do with the weather stripping around the vent door on the heater box. Same thing happened to my 02 a year or so ago.

I have a friend with an 99 GMC, he picked me up from the airport one night, it

was -30C and my feet where froze stiff by the time I got home (1.5 hrs),

Another friend works for a GM dealer, said that there is a plastic plug that when it comes out in behind dash/firewall lets outside air in,