The most likely scenario here is that you got a big wad-o-soot in there. The high insolubles with the high viscosity point to that. Do you have other UOAs to compare this to? Seems like a lot of soot for just 2900 miles, even considering nine hours of high idle. Oxidation can also cause high insols and an increase in viscosity. Because you didn't get the TBN test, we can't tell much about that. If it was oxidation, the TBN would read very low. But it seems more likely it's soot that oxidation. Wear metals are very low (and should be at such low miles).
The one thing I don't like about Blackstone report on diesels is that you don't get a separate soot number.
You can get a big soot load by lugging the engine, overfueling from a problem with the fuel system, or modifications, or a defective EGR system (if equipped) or plugged exhaust and possibly a turbo problem(exhaust blowing into the lube circuit of the turbo). I suppose it's possible idling could do it but in my limited experience, you usually see fuel dilution, not soot.
Some ideas to cogitate, anyway.
