GTO twin turbo vacuum leak

So I got my gleaming polished intake plenum today from 3sx...swapped it out with my old one, and now my car runs like a pile. It stalls if you dont give it gas. I noticed that when I romped on it though, that my boost guage would drop dramatically as my turbos spooled. Ok, so vaccuum leak I figured. Theres some sort of sensor tagged onto a line coming from the top of the plenum itselft (it's also 'tee'ed' to go to my boost guage). Its mounted on the friewall close to the battery, and has 3 outets. Is this for the factory boost guage? anywho, I noticed that after hooking that up, there was an extra port on it that felt like vaccuum on the bottom (facing down towards the engine). Im pretty sure that I hooked it up right, but does anyone have any info about this piece and where it is supposed to go?

You must have forgot to hook up one of the vac. lines.  Can you get a picture of the open port that you speak of? 

The factory boost gauge does not read vacuum/boost.  It gets its information from the ECU, it only shows where the ECU "thinks" the boost would be.  It is more of a engine load guage than a boost guage.

ok so I got my baby running. I really had no idea that the EGR valve block plate (on the firewall side of the plenum) had a gasket. I looked at my old plenum and noticed a mashed ugly little piece of metal that used to be a gasket. Freighted a new one in from cali overnight, slapped er on, and away I go! Yay, problem solved for under $10! that's not common with these cars hahah.

...I love it when it's an easy (and cheap) fix.