The romp is often blammed on "stichion", but that is a separate (and over-blamed and misunderstood) issue.
The romp is generally associated with the interaction of the lube and the FICM or PCM or whatever term you prefer (model year dependent). Because HEUI is depending on the oil to provide injection pressure, the thicker cold oil reacts slower at start up, and somewhat hinders the injection rates. The computer, in turn, tries to "adjust" and compensate for this and increases injection commands. That in turn ups oil pressure from the HPOP, and (in a sense) over-revs what the desired idle speed would be, so the computer adjusts it back down. Hence, the romping, cyclical idle until the oil warms up a bit. I've heard it be longer in cycle in some trucks, and shorter in others. Both the time to "normal", and cycle frequency, kind of depend on the individual truck and lube load. It's really annoying, but also harmless, essentially.
Why is shows up at certain times in vehicle life, and yet not others, it is beyond me (and others) to describe accurately. It just happens.
Generally, lubes with lower vis specs will help solve (or at least reduce) the romp in cold weather. My neighbors 6.0L PSD would romp on 15w-40, but was greatly reduced on dino 10w-30. The issue is very similar with the 7.3L PSD. The real difference between the 7.3L and 6.0L is that the older 7.3 uses oil to lift the injector pintle and a spring to close it, whereas the 6.0L uses oil pressure to achieve both tasks. But I've heard romping in both, and it's mentally bothersome. Won't hurt a thing, though.