I don't have this problem. I have a 2SS manual and I drive like a rock star (i.e. fast and with a narrow margin of error.) Don't tell the insurance company I said that ;-)
There are lots and lots of things that cause misfires (
http://www.2carpros.com/first_things..._run_rough.htm) It's troubling in such a new car though. I have heard that the electronics on these things are on par with the space shuttle.
Are you putting cheapo gas in it? The V8 requires 91 or higher. GM claims that the computer will retard the spark to compensate for lower octane (Most modern cars can do that) but I wouldn't chance it. If I could find 93 around here I'd use it.
As for the mechanic driving it home that is actually a really good sign. It means that they are willing to go the extra mile to find out what is wrong. The bad ones will just try to tell you that you're making it up.
Depending on the laws in the state you are in, if you keep having trouble you might get them to take that one back as a lemon. Then you can get a 2SS and not drive it like a wuss. That's working for me :-D