DTC Code P2463 Duramax DPF Filter - Soot Accumulation

My truck will not go into the automatic Regeneration to clean the Diesel Particulate Filter (DPF). Check Engine Light came on, it is throwing code P2463 DPF Soot Accumulation. My scanner shows back pressure is only 0.1 PSI at idle, and normal driving around 2,000 RPM it reaches a high of only 1.17 PSI.
It usually does a Regen about once per tank of fuel, (elevated idle speed of 800 instead of 640RPM for about 20 miles or so). But it is not entering regen.
Now it goes into the power-limiting mode after about a minute of driving.
When in the limp mode, it will definitely not get the exhaust hot enough to regen. And without a Regen, it will not clean the DPF. Vicious circle.
Any ideas on how to get it to clean the DPF? Thanks. Truck has 114K miles on it now. I have heard GM extended the Emissions Warranty on the diesels to 120K, but not sure what years or models?

This seems like a chicken and egg quandry. Is the truck still under its powertrain warranty?