1995 gmc jimmy - vents don't blow much air ?

The heater or blower for vents and defrost in my 1995 gmc jimmy 4 door suv don't blow air for crap. On the high setting it just blows enough to feel it if you have your hand right in front of the vents or defrost vents on the dash. Do you think a vent is blocked maybe or partially blocked ? I'm not sure its the blower motor seems to work fine unless someone knows of a stronger blower motor that would fit into the 95 jimmy ?