I am by no means an expert on diesels but I am very well acquainted with service manager at local GMC dealer where I have purchased several vehicles.  I was there one day when one came in on the wrecker.  His said far and above the biggest problems he sees is that owners don't change the fuel filters often enough and that was the first thing they were going to do with this truck.    He says the customer will say, it just change is 6 months ago!     When was the last time you service the fuel filter?