How long ago did you install the kit?
Did you purchase it brand new?
Have you returned the headers to HPP? There is a fix for it.
Also, are you using the turbo support brackets that bolt to the timing cover?
The kit was bought in 08 and I brought it on the car in 2010. That set cracked in 2011 and then another set cracked again in a different spot a year later. And yes I am using the support brackets. They didn't tell me about any fix for it.