K1500 missing vacuum line?

I'm hoping someone can tell me if I have a missing vacuum line on my 5.0, 1996. On the passenger side of the engine there is a vacuum switch that appears to be missing the operating port tubing. It looks like this switch lets the gas vapors from the cannister go into the engine. The port in question has a rubber elbow on it but no plastic tubing is inserted into the elbow. When I apply suction to this port it feels like I'm pulling against a diaphram. The other 2 ports are hooked up. There is also no emissions label on the radiator support. Any help would be appreciated. 

yeah, i would assume there should be something there, but i have no clue what. vacuum lines are the devil, so i denounce them in Jesus name, as the Bible teaches.

Is your truck running bad, or did you just notice it one day? 

I was looking into an elusive stalling problem when I noticed the missing? tubing. I was checking on the fuel pressure, which drops to about 55 to 56 lbs after start-up. I know the pressure regulator is vacuum sensitive and started checking for a leak. 

There is not missing vacuum, hose, this is the way the switch is designed, this port will sometimes have a small square piece of foam over it to filter atmospheric O2 it draws in but the foam can deteriorate over time and fall off.BTW your fuel pressures are within spec's as well.

That stalling problem is still with me at times. It happens almost every morning, when I first leave for work. Truck starts just fine and will idle as long as I want. The trouble starts when I Put it in gear, forward or reverse.
 
The truck moves just fine for about 2 seconds then it stalls. Once it does this it is harder to start the second time, and can idle really rough for a few seconds. It may stall a couple of times like this then will run good all the way to work.
 
Same thing happens when I leave work at end of the day. The truck is a '96 K1500 with a 305 engine and automatic trans and has about 85,000 miles on it. It has a new fuel filter and air filter. The fuel pump has been changed twice in the last 4 months. Think I'll pick up a vacuum gauge tomorrow but would also appreciate any suggestions.