Truck has no power then surges
 

I have a friend who owns a 2002 Dodge pickup with the 24 valve Cummins diesel engine. I told him to post on an internet forum, but he doesn't use the internet, so I said I would post on a forum to see if anyone could help or would know what to look for. The issue he has with his truck is that it will run with low power, then it will surge with normal power. He brought the truck into local mechanic who changed the fuel filters and changed lift pump and charged him $500 plus dollars only to have it running the same exact way. My friend thought it a chip problem, but after reading the forum I am thinking it has something to do with fuel system.

Has anyone ever experienced something like this or can anyone help my friend with advice as to what this could be or what to look for? It would be most appreciated. Thanks