Thanks all for your input.
My friend who owns this truck did a bunch of research. Checked online to see what other owners of diesel Colorado/Canyon owned were experiencing, and nobody else had trouble with cold temps. That's why I disregarded some of the advice in the other thread regarding the DEF freezing.
We also saw plenty of trucks like ours... Easily identifiable by the little Duramax Diesel badge. None of these had those grille covers or anything. And I doubt all these people are driving around with check engine lights.
After we zip tied cardboard to the grille and romped on it a little bit, and were able to keep the coolant temps about 10 degrees higher than before, we cleared the codes. It seemed to be attempting a regen at that point (EGTs about 800 and 15mpg instant fuel economy). Unfortunately about 30 miles later the check engine light came back and we have the P244C and P24A0 codes. However, the P244A code that was resulting in reduced engine power didn't come back, which was nice.
If I understand correctly, if the truck can't regen the DPF will get clogged. And the truck won't work anymore!? Sounds like it's time to take it to a dealer because this truck is under warranty and we can't have it suddenly stop driving in these temps.
We called a Chevy dealer and told them the codes and what was happening and the service guy straight up said "you should call GMC roadside assistance because it's their problem, not yours" sounds like he was right. We'll call GM when my friend wakes up.
PS: In the meantime this just looks ridiculous! I feel like my 300K mile Suburban would have handled this trip better than this fancy truck LOL.