Okay I've done some searching and seen that these two issues come hand-in-hand apparently.
[ul][*] Hissing under the hood.[*] No air from the vents.
[/ul]

Okay it seems to me that the hissing is coming from some place near the distributor cap. That and I have no air OR heat coming from the vents on the dash. It comes from the floorboard and the defrost vents though. I've checked the plastic ball-shaped vacuum pump and line it seems fine to me. No holes or leaks anywhere that I know of.

I drive a 1994 2WD GMC Jimmy VIN W. Anyone have any good ideas or suggestions?

 

You are not getting proper vacuum supply to the HVAC system. The hissing indicates that you have a vacuum leak which is what is causing the HVAC problems.

 

check the hose that comes off the back of the plenum and goes to a 3 or 4 or 5 way connector-bet you have no cruise either. jp

 

Any ideas on what to look for... possibly spraying the hose with soapy water and checking for bubbles?

 

There will be a small black hard vaccum line that runs into the cab right around the dizzy, make sure its not broken, cracked, or missing and still hooked up.

 

Some carb cleaner or an unlit propane torch make for the best vacuum leak finder. With the engine running, trace along all of the vacuum lines until you hear a change in the idle speed/sound.

Soap won't do anything as it is engine vacuum in these lines, so it is pulling air in...

 

Sounds to me that if I get a can of carb cleaner and spray it along the lines, if I come across a point of cracking or something the engine will change in idle speed. Worth something to do tomorrow. Appreciate it man.