[MagicRat]

If you lose blower fins, then the blower motor goes out of balance and may make a noticeable vibration.
Low air flow has been caused by misaligned, leaking or disconnected ducts.
Take a look at all the ductwork behind the dash. Make sure its all nice and tight. Use duct tape to seal any airleaks if necessary.
Also, my Jeep had debris blocking the fins on outside of the heater core, causing low airflow. I had to remove the heater core and blow it out with compressed air. The AC evaporater can also get blocked and cause the same trouble.

As for the groaning, I think you have a rear differential on the truck. Check the fluid in the diff housing. Replace it with fluid intended for positraction differentials, if necessary. If you do this, the noise may not go away immediatly, but should eventually quieten down.