My truck has begun displaying a "Reduced Engine Power" message in the DIC and begun running like crap. It hesitates on acceleration and feels like it is missing and not firing on all eight cylinders. It has done this once in the past, but it went away when I shut the truck down and restarted. It now seems to be here to stay. It does it when the truck is warm or cold. The check engine light does not come on, just the message in the DIC. I have no code reader to check on codes. Does anyone know what would be causing this? I would appreciate any help that you guys might have. Thanks!

Goto a an autoparts store and have the codes read and write them done. That be the start.

Brian

When's the last time you changed the fuel filter? Duramax is pretty finicky when the fuel filter gets clogged.

I have the same problem. mine is most likely the app sensor or accelerator positioning sensor. Like a hundred tollar part.