Duramax surging

[jet]

A good friend of mine has a problem with his truck surging as it goes down the highway. Does this with the cruise on or off. Has a performance chip in his truck but it does it with it in or out. Has changed the fuel filter several times but it won't go away. Truck is an 03 4x4 crew dmax.
There is a wealth of knowledge on this board and I hope you have some suggestions on what the problem might be?

[More Power]

With or without cruise?

MP

[Nix]

Jet, does the truck do this while idling? If so I had the same problem and it turned out to be the fuel pressure regulator which is covered under the 100K engine warranty so don't let the stealership tell you otherwise. Good luck!

[madmatt]

to add to NIX post.. if it's under 8yr/80K federal emissons will cover it, no deduct. make sure to ask your dealer about this, most just run it under factory warr not knowing/ caring.

[jet]

Truck does not surge at an idle only at highway speeds. It does this with the cruise on or off.
Could it be something in the tranny?

Thanks!

Jet