Dead battery I think

Yeah I've been in that negative 30, not wise to shut it off

 

-30° can kill GOOD batteries

 

Don't think he said negative 30, just below 30.

Anyway, what you describe "feels" like a bad connection. Start by cleaning the connections at the batteries (including the posts). They make a spray that helps keep corrosion off in the future. Then check connections to the starter and the ground to the frame. Both can be problematic. At 12.8 volts, the truck SHOULD crank and start just fine (but your mileage may vary). Now, it the temp was truly 30 below, yeah, all bets are off. Anytime it gets close to 0, starting diesels becomes unpredictable, unless plugged in and you have something like a Davco that pre-heats the fuel.

 

The -30° comment was to the two post right before mine.

Yes the op said below 30°

 

Was up in Northern Saskatchewan

 

I remember losing a little something against really cold weather over the years. Thats one benefit of living in the south, aint too bad yet.