I was curious if anyone knew where the cab air filter would be located at. I attempted to search for it in the FSM and didn't see anything for it. I found these on a site, they are replacement cab interior air filter.
http://www.genosgarage.com/prodinfo.asp?number=CFF-DG-0611R
http://www.genosgarage.com/prodinfo.asp?number=CFF-DG-0611R