Gotta be upper intake gaskets chevy bad for that!

 

well bumpin the last time I had the monte in the dealer for that key recall they said the whole engine needs to be pulled and torn down and all the gaskets replaced. they said the head gaskets are fine but all the other gaskets and three of the injectors need to be replaced as well as the fuel pressure regulatior. they also said if I didn't want to do that we can get you in another car

 

You might want to get a second opinion. This is most likely Intake Manifold Gaskets, just had mine done. I couldn't get the McDonalds drive thru with out it overheating.
The Chevy Dealer wanted about 2100.00 for this job my local shop that I have used for years did it for 600.00.
You can also see the same thing if you YouTube the process. Hope that helps. butch049 is right.