try this out
I have a 2002 crew cab 1500 hd with all the stuff. Dusty in the dessert, change mine often. If is the same as mine, there is a thin rectangular cover, that has a angle or fold that wraps over one edge over the duct work under the glove box. Three bolts ( actually screws with bolt head s) I think 6 or 8 mm....remove these and take the cover off, use a needle nose pliars to grip and slide the first one out, then reach in and grab the other one, slide it over to the opening and do the same. Can also use hemostats...while it is open take a little compressed air and clean out...get them in with the air flow going the right direction as you would on home furnace filters. You should get a lot better flow through your vents now.