Both batteries were replaced about 3 months ago. The first time it did this was in November, before they were replaced.

You can check the EGR valve to see if is sticking . Remove the four screws that holds the motor on , The valve has a keeper like a valve spring . Then you can push on the valve and see if it moves free in and out. Sometimes just working them some is enough to free them up.

Ben, I don't know if KY has emission inspections or not, but I'm wondering if there is any way to bypass/delete the EGR function, even just temporarily, for diagnostic purposes?
I was thinking that your friend may be right about the DPF needing to be replaced, but TD3550 has raised some good questions that might point toward the EGR system...

KY did away with emission inspections about 15 years ago. So, I already have an appointment on Wednesday to delete the DPF and disable the EGR. If it never gives me trouble again, I'll know that fixed the problem, whatever it was. But without a complete diagnosis, there's no guarantee that it's a cure.

Checking for a sticking EGR sounds simple-enough. If I don't have to work this weekend, I'll give it a look.

I'm about 90% confident that this is emissions related, but I could be basing that on coincidence... That's my fear. It did a regen on my way to work this morning, with no problem. I'd rather leave all the emissions equipment intact, if it worked properly and a replacement DPF wasn't so expensive!

Again, thanks for all of the insight and suggestions.