lack of air flow....

Is it possible that my evaporator core is so plugged that it won't allow any air flow through it into the car? Not the inside of it obviously but the external fins of it? I pulled the fan motor an d yikes was it dirty...(kind of gross actually?).The fan is going full bore but not getting to much inside...It feels like it is switching between defrost and heater when I select it...not pulling any body error code either. Has any one else delt with this kind issue? I must get a buick factory service manual!ebay here i come!
Any help would be appreciated!

Has your ambient temp been consistently below freezing (32* F) lately.
If the HVAC feels or sounds like it's going between Defrost and heater constantly while running, it could be the drain tube is plugged and the moisture that is collecting in the HVAC / Evaporator may be frozen.
Do you have a garage to heat it up in and see if operates OK above 0*C.
Try unplugging the drain tube located under the car below HVAC system. Use a piece of solid wire or a section of coat hanger to probe the hole in the Black rubber nipple that hangs down. If it is plugged with crap and/or frozen you will experience what you are experiencing.
Also, if your fan motor was all covered with crap, an abnormal amount of crap, then your evaporator may also be in the same condition and might need to come out for a cleaning unless there is a way to douche it while it's installed. I don't know. I would start with the easy part first. That is trying to be sure the drain port is clear and there is no water freezing inside the plenum.

I found that the evaporater core was plugged with dirt etc....I will replace it in the spring.But for now i just removed the blower motor resistor module and took my air compressor and blew it out. Again will fix properly in the spring.But LOTS of air flow now!! Onward to the next problem....