1996 Tahoe Air Movement

Need some advice and/or help.  I just purchased a 96 Tahoe that is in great condition except for the amount of air coming out of the vents when the fan is turned up.  The blower sounds like it is blowing hard, but there isn't much coming out of the vents even on HI.  I think there maybe a dampner problem where the direction of the air is not being opened all the way.  I don't know what area that would be in.  Also, when the A/C is on and the direction is set to blow only on the top vents, condinsation spots will show up on the windshield where the defrost would usually blow.
 
Thanks

I had a similar air flow problum. Mine had a plastic grocery bag sucked into the air intake. Just reach up behind the blower motor & check if it is clear.