Crack each injector line one at a time until you find the misbehaving cylinder and go from there. It could be an injector, weak compression, valve who knows.

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Only diesels in this driveway.
2005 E320 CDI 243k Black/Black
2008 Chevy 3500HD Duramax 340k
2004 Chevy 2500HD Duramax 220k