I've happened on a method to spot the Diesel Particulate Filter regeneration
The intake air temperature on the ScanGauge goes way up when the regeneration is happening (these days it's < 5° to almost 50° C / 32 to 122 F).
And I've found a few more stretches of road where I can coast.
They're in 20 and 30 mph zones, where I usually get my worst mileage.