update
 

thanks for the info. Just waiting on winter to get over with among other projects. I'm going to check the performance upgrade sensor wiring and vacuum hoses before I tear into the turbo. It runs ok and has boost as long as I don't stay in the throttle for long. If I do, the turbo shuts off and runs as a 4 cylinder. Push clutch in, cycle ignition off and back on, and get boost back. I still think its one of the sensors instead of the turbo itself but I'm clueless how to check them. That's all for now.

Give this a read, title is not what you're looking for, but the discussion is worthwhile.

https://www.chevyhhr.net/forums/ss-s...estions-55719/

And, for what it's worth, a summary of MY recent experience:
although it's not exactly how you describe, it's similar.

I would show up to 1.8lbs boost for about 1/4 second, then it would drop to 0 and continue to drive like a 4 cylinder car. The check engine light would show up eventually, with code 0299 plus more. (I didn't see any difference after turning off key in the way you see yours "reset.")

I inspected as well as I could, but a mechanic noticed a looong crack in the intercooler output (cool side) charge pipe. He put a BandAid on it (two hose clamps - one on elbow leading upwards to intake and one higher up near the intake), and the boost goes to 11lbs now and I hear wooshing (likely my new "BandAid Wastegate" that can't hold more than 11). No more check engine lights, lots of fun torque steer.

It might be that you have a crack that is not as significant as mine, which allows for more/longer boost and possibly allows for that resetting phenomenon. I really don't know how these computers work... but the Chevy dealer in Tulsa told me the same thing: likely the turbo went bad.

A smoke test might be an excellent idea. If it's your intercooler outlet pipe, I found one for $115 shipped. (Showed up yesterday, hoping to install today or tomorrow!)

Funny how so many different problems can have similar symptoms. I sure hope you find it easily! Thanks for updating the thread, too - please do keep us updated for the next Hapless 0299 Victim.

Roger that