Well, I feel silly.

I am sure I checked all of the fuses over once the night that the truck first shut down. Since then, I've been focusing on the relays and fuses for the fuel pumps and ECU.

Turns out, I missed a fuse in my initial inspection, and then never thought to look at it again since the description didn't prompt me to look into it further.

Fuse #22 was my culprit. So it was that the ECU was dead. It was just a problem with the power to the ECU relay coil circuit. I found a wire that was bare at the coil that must have been chewed on by a rodent that was touching the metal bracket around the coil.

I didn't grab a picture and ran out of time to look into the connector further, but I'll have to wrap it in electrical tape for now. It's not the two wire connector that plugs into the coil directly, but the single-wire (grey??) connector separate from the coil but in the same loom.

I'd like to figure out how to pull the pin out of the connector and replace the wire since about a 4" section is missing insulation and it's right up against the connector so wrapping in tape won't cover it the best (or look nice).