Sound like the EGR cooler? That was the same thing mine was doing last year. I knew when we were talking at hooters you had issues, but I thought that was a return visit when you took it back. My mistake. Is there white residue by the coolant reservoir? mine had that and I thought I had a head gasket issue, turned out to be the egr cooler/oil cooler.

Hopefully they will get it resolved for you, and soon. If you have service records showing that you had it in several times for the same concern and they did not check it out properly then you should not have any issues trying to get for to cover the repairs. Stay vigilant and keep going higher up.

Good luck Tim.