I figured out a way to stabilize the wild vents. Total cost, $24.00 Total time 20 min. Non invasive, no heavy wrenching required. I took pics, and as soon as I can get them on my computer I will post.
This is not a fix for the root cause(intake) but I figured it out to get my vents working correctly until I have time to tear down the truck, which, with my schedule, will be a while. I even have the part numbers!
Upside. This can stay on, even when you fix the intake leak.

 

I got it from NAPA, because my wife works there...google GM vacuum reservoir.


This is the part. The large nipple goes to Vac source. It has a built in check valve. Bonus!


Two different sized vac line. The large goes to source. I forgot what sizes they were. However, I should have got the next size smaller in the smaller hose. I had adapters, so it wasn't a problem.

 

Where will will make our connections. See the T buried back there?

 

The Hoses. At the T, disconnect the hose that feeds the blend doors. Your large hose will connect to the T, it's the larger nipple.

 

Mounting screws installed

 

Hoses attached and cut to length. I ran them behind the ECM


Bolted in place.

 

Plenty of room.


Bolted in place.

 

Drove it last night. Vents staying stable when I give it the gas. I suspect that if I was towing, on a long incline, eventually the reservoir would deplete. But, so far, I'm happy to have the cold air blowing where I want it. And it was cheap, and fast.
Pricing reflected was an average. I actually spent 14.00 bucks total. I had some adapters already, I needed 1. And I have a box of self tapping screws. Did I mention my wife works for NAPA? Employee discount baby!!

 

Good job on the work around!

Or for just $14, you could have fixed the vents with OEM check valves:

 

You missed my point.
My problem isn't the check valves, it's the intake. All vacuum valves leak, some more than others. So you need a constant vac source, even with a check valve. When your source is intermittent, like mine, and many others, the blend doors go nuts. This gives you a reservoir of vacuum, for those times when you are hard on it, and your vac source disappears. Think of it as a car battery. Power in, power out, but when the power in stops, you still have a reserve of power out.