You might want to open the front of the furnace and take a look at the plenum, mine had dropped. I pulled the ductwork up and reattached it. I also made a sleeve to cover the exposed wood. I also blocked off a portion of the vent dumping into the belly as there is no ductwork attached to it and it will take the most air. Caution: Before blocking anything or throttling your vents down, look at the paperwork for the furnace and they should list a minimum number of ducts needed to operate the furnace safely.
Goody Two Shoes and the Filthy Beast
2008 Chevy Silverado 2500HD
Duramax and Allison 6 speed
2012 Wildcat 282RKX
You can't make things idiot proof, you can only make them idiot resistant.