Hey Guys,
I spent some time with the shop forman yesterday at our local GM Dealership.
One of the things I questioned him about was when the Vin K intake pleanum
was improved / upgraded.
He said it was definitely upgraded to a higher heat resistant material but couldn't
remember what year it was. This explains why the current plenum is not thicker like the Dorman.
He suggested I check with the parts staff when they get in tomorrow as it was after
hours. As soon as I could find out moore I will add to this post.

I've heard rumors that the 2000+ vin k'* have the improved upper intakes. I'm hoping this is true. I'm on my way to finding out.

It would be nice if they do and you could swap them out.!

As a few of us on this forum have learned, they're definitely not improved as of 1999.

I have found no infomation on the OEM upper being upgraded to a stronger or higher temp material. But somewhere along the line I believe starting it 2000 or so they made the EGR tube sticking up from the lower intake smaller. This puts an air gap between the EGR tube and the upper intake which reduces the amount of heat transfered from the tube to the pleanum.

Check your white ID tag near the PCV cover.
If it is a Rochester product its the original design.
If it is a Delphi its the improved design that a GM shop forman said is
higher heat resistant.
My 2001 used replacement is a Delphi so its improved.
The korean dorman .......who knows?