Glad you found that! However, I would still strongly recommend you replace all the other plugs. The other ones may also be damaged, though not visibly, and be a continuance to your headaches. They're inexpensive enough that change them and using a cushioned socket would be extremely ideal.

again usually a missfire will set a code and the gm mechanic would have been able to see a code for a missfire!!!!

I think you are on the right track seeing as a vacume leak can cause a egr code to pop up!

I think we've covered the misfire already. My statement was preventative, not causal. I don't think he'* getting any symptoms from the plugs...yet. But he did mention that he changed 2 cracked plugs that cracked during installation using a bad socket. Usually, more than just two will be cracked in this case, and can start to cause issues fairly soon.

I was commenting to Richs00ssei statement as to the missfire.

I agree it is good preventative maint!!!

Hehe, my apologies.