IIRC it only does this if you have removed the dpf. As long as the dpf is in place it needs to regen. If it is gone you must have the extra fueling removed from the tune. You can have stage2 with or without the dpf in place from my understanding. When cold it will also fast idle.
I forgot to mention in my OP that the DPF was deleted as well.
Last night was the first time I really observed this behavior in detail. It was also very cold; about 24F at the time I noticed and the car had only been idling for about 7-10 minutes total. So, coolant and block still had not reached optimal temperature.
Basically, I was sitting in the car looking at my phone when I noticed that RPM suddenly and quickly jumped from 800 to 1000 RPM. What had me baffled was that the car had been idling at 800 for about 7-8 minutes by that time. If the RPM increased due to a fast idle request from the ECU due to ambient temperature, wouldn't it happen right at engine start? This is why I thought it seemed more like a regen operation. I did not notice the cooling fans kick on which would normally happen during an actual regen cycle.
I guess I better call Diesel Dubs or Malone to ensure that the extra fueling was removed from the tune, although I'd assume that to be the case since the DPF is gone and I don't have any fault codes stored.
Edit: I also had cabin heat on full blast; could a fast idle condition have started because of that?