My '06 Cobalt had that problem (BCM) the day I drove it off the lot at approximately 26,000 miles. Since then, it's been in the shop 7 times. Their newest idea on how to fix it (being that the BCM was replaced/reprogrammed (whatever) three times already (once before I even bought it!) is to rip apart the transmission.
I escalated the problem up through GM and all of it is warranty work now at 41,000 miles.
I hate this car.
If you've had any similar problems occurring before your warranty ran out, look into your state lemon law. I bought mine in Texas, which doesn't cover used vehicles, but perhaps for you it will be different. Good Luck.