I'm confident things like waiting at lights and stop signs, coming down mountain passes, and cruising along flat interstates, are what's causing such high idle times on the hour meter.
I looked a few weeks ago when my odometer went over 3,000 miles. At that point I had 27% of engine time recorded as idle. Now at about 3,500 miles it is still at 27%. I pretty much never drive in stop and go traffic and also encounter very few red lights. Probably 85 to 90+% of the miles after the first five hundred or so are towing. Also when I start it up I always try to high idle it. So I think most of my non high idle hours are when unhooking and hooking up the TT and that is sure nowhere near 27% of engine time. Because I have so many idle hours even with my driving characteristics, I suspect a couple of things. First, maybe high idling the engine is still counted as idle time. Also some of my driving time must be counted as idle time so maybe coasting down hills also counts and other times when the rpms drop adds in to it. I have no way of knowing for sure what is counting in to the total. But I am sure that my "traditional" idle time is not really 27%.
All that being said, I don't really think any issue is being caused by my high idle time. My DPF gauge is always on 0%. Or so close to 0% that it looks like 0%. I have only had three regens so far, at 24 hour intervals. So I am only getting the automatic regens that happen whether the DPF needs it or not. I am about 2 hours from my next regen and the DPF gauge still is on 0%. Also the DEF just went below 1/2 so I can now fit a box into the tank without overfilling it which I will do before I head out on my next towing trip. I would estimate that I have used about 12 gallons of DEF in 3500 miles. Almost all towing and 3 regens. I can't be positive about the DEF mileage as I did not track it for the first thousand miles or so and am going by memory. I will note the mileage and gauge position when I put in this next 2.5 gallons and see how far I go until I get the gauge down to that point again.