A guy I work with has an '05 GMC Sierra with the Duramax diesel. It's been skipping out at around 50-55 mph, engine shudders and runs rough. The dealer told him that 4 of the injectors are bad. They suggest replacing all of them, to the tune of around $6K! The truck only has 140,000 on the odometer, not what one considers high mileage on a diesel. Doesn't sound right, does it?