Hi,
Sounds like you may be suffering from stiction. It is the most common cause of performance issues and injector failure in the 6.0.
We make a product called Hot Shot's Secret that was tested by International and proven to fix this issue. You can see us on the web at
Lubrication Specialties | Diesel Motor Oil | Primrose Engine Oil | Fuel Additives | Oil Additives | Engine Restore|. The product works well and is 100% guaranteed.
If you have questions you can give us a call at 419-768-2647 during regular business hours or just send us an email! Good Luck.