I do know about cruising down the highway but it didn't work.

It's -20 c here,my truck has idled quite a bit for the last 2 days,we do travel down the highway for a little ways before turning down oilfield roads where we can travel 50mph for most of the way,well tonight the overhead console flashed 80% full so i tried to maintain 50mph as much as possible and 60mph on highway but it jumped to 90% on overhead and DPF FULL reading on odometer area.

WTF now?