[GMMerlin]

Sorry to hear about your automotive woes.

Unfortunatly you can not just demand a new car. There are Lemon Laws to help with your situation.

First thing is to determine what happened. If this problem happened twice in 3 weeks, be prepared to leave the car long enough to have the technician duplicate the condition.
Intermittant problems are very difficult to diagnos and repair and do take a considerable amount of time to find.
Here is what you do.
Don't show your ass at the service department! its not their fault your car has problems, They are there to assist you.
If you drive the car in and the problem is intermittant do you really think they are going to find the problem right away? probally not.
Be prepared to leave the car for a couple days and ask about a rental (GM supplies rentals at no charge to you under certain circumstances)
Give the service advisor as much information as you can about when the problem occurs and what happens (be calm and professional ! make sure the advisor listens to you and writes everything down)
If the service manager is available talk to him about your problem and let him know that you would like to leave it for a couple days for diagnosis and ask him to touch base with you.
If the service advisor or manager calls you back and says they did not find anything wrong with your vehicle, ask him if they checked with technical assistance or the GM technicians forum.
Make sure the car has about a 1/2 tank of gas...if they have to drive the car there is gas in it and if the tech has to remove the fuel tank..its easier to remove.........(Personally I hate when customers leave the tank empty or have it slammed full)

Mostly, be Patient! If you want your new car repaired properly and your confidence restored in your GM product give the service department and the technician working on it some time to find and repair your problem.
Understand that the service department and the tech did not design or build the vehicle...they are the people that have to find and repair the problems.