There is no cabin filter, and its tough to diagnose without being there in person, I know the blower system isn't real impressive anyway but it should keep you cool. I don't know what the 6.0's had so there is a SLIGHT chance this is normal. Compare it to a like truck if you can.
But lets work on the assumption something is wrong.
Are you getting air out of the correct vents? If not could be a blend door issue.
Do you have the dual climate controller or the rotary dial type?
Are all your air flow settings working, IE does the fan speed up each time a higher fan speed is selected? (clear as mud right?) If not could be the blower motor resistor.
If none of the above applies you would need to see if your getting correct Voltage/Amperage to the blower motor itself, I'm afraid I don't know the specs.
If your getting the correct voltage/amperage, its probably a bad blower motor. (or some obstruction in the duct work, but unless you have a mouse problem its probably not that)
Last edited by 44magnum; 09-09-2012 at 08:04 PM.