Help! Isx cummins with skipping issues

[DieHard]

Hey there, I have a 2004 Volvo vnl with a isx dual cam cummins. I bought the truck about 9 months ago and I cannot figure out why it is skipping. I had a new head put on it and had the overhead ran 3 times, put in new injectors and still skipping. Running down the road, I have no issues, but when I idle, it skips. Some days are worse than others tht it skips so bad it shakes the truck. Took to a few shops and no1 can figure it out. I have zero fault codes. Thx for ur help![/b]