Just sounds like a tired engine to me. If a diesel has a hard time starting in cold it has poor compression or bad glow plugs. The trip and hauling the trailer might have accelerated the wear even more.

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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