On the furnace, take the duct(s) loose at the unit and see if the knock-outs have been removed. If they have, fire up the furnace and see how much air comes out the discharges. If the blower is putting out plenty of air then you either have a plugged up duct or it's disconnected somewhere in the underbelly (I'm assuming you have an enclosed underbelly). You may have to remove some of the covering to find where it's blocked or unhooked.
As for the A/C, Pull the grill off and take an inspection mirror and see how for you can see down the ducts. There could be a piece of Styrofoam or something blocking them.
Salem 29RKSS Pushing a 2500 Mega-Cab CTD!
Gotta go campin!