Well, you guys appear to be right on the vacuum leak. After I put on a new EGR valve I found on ebay, & still had the same rough idle & real gassy exhaust smell, I took it back into the GM shop &, after saying that the smell was from the washer fluid jug, there was the tube completely broken off.
It'* the black tube that runs from the supercharger past the left of the air cleaner (as you're facing it from the front). Anybody know what that is, where it goes from the SC?
Anyway, he slapped a little piece of hose over the break in the tube. I was a little concerned about the fit & whether that was a good seal, but it doesn't seem to rev when I spray carb cleaner around it.
The engine wasn't turning over without pushing down the gas pedal some, & seems like a high-pitched hiss sound coming from somewhere, but I'll monitor the situation. Seems to have gotten rid of the gassy smell & idles better (I think/hope).