Surging when setting still

[Jethro6213]

A guy I work with has an '05 GMC with the Duramax and the Allison auto. He said it has started surging when he stops at a traffic light. He said it only does it in drive. He has an Edge hooked up to his truck. He asked me what could be the problem, but I'm not familiar with the Duramax. Thanks for any help you can give.

 

[JD4440]

First guess would be fuel pressure regulator