My last work truck had the 6.4 in it, by 80k miles it needed a quart a week. If it was my personal I would have investigated further, it was babied it’s whole life though. Left me with a little fear of the 392…
I hit my first oil change based on miles. I added about half a quart during that break-in period. Since then I've got another 2000 miles and still on the full mark.
For better or worse, I take the 6 month OCI requirement with a grain of salt. For a vehicle that doesn't make mileage due to short trip driving I would absolutely change in 6 months due to possible moisture contamination and any potential acidity build-up.
Conversely, for our vehicles that alternate between being parked and taking longer trips (where the engine spends an extended time at full operating temperature) I change based on mileage even if it goes past the 6 months. To me it seems improbable that 'time being parked' is likely to cause any serious degradation of the oil.
It would be interesting to hear what people have found using lab oil analysis with respect to their driving habits and their conclusions about time based OCI.