Engine temp 170.

When the shop gonna have computer plugged in to your truck ask them to do compression test(do it couple times better 3 times) and injector balancing. Take a pictures, this tests will tell you little bit more info about health of your engine.

 

Idling a truck in cold weather at idle, 600 rpm, is no good for your engine.
Your idle should be set at 800 to 1100 rpm depending how cold it is, not only to keep the engine warm, but to keep a proper flow of oil to the turbo and other parts.

Chugging away all night at low rpm in real cold can lead to premature death for a diesel engine.
The engine never get's warm enough for the piston rings to expand enough to create a proper seal and fuel dribbles past the rings, into your oil and out the exhaust.
If you see oil slobbering out your stack or anywhere else it's because your engine is probably running too cold.

The computer engines are a lot better at holding an idle and their heat than the old engines were because they monitor and protect themselves, maybe the reason your idle increased while you slept.

Pull your dipstick and have a sniff, bet it smells like diesel fuel.
If it does, think about what that fuel is doing to the inside of the engine, other than dissolving crud and washing your cylinder walls with fuel which can lead to excess oil consumption because of the polishing effect on the rings and liners.

Back in the day, my Canadian compadres and I could easily spot a trucker with no clues about the cold.

Their truck would be chugging away at 600 rpm in -30º weather, the stacks were black from oil and unburnt fuel slobbering out the top and there was a puddle on the ground.
We would bet on how far they made it out of the driveway before their #2 fuel jelled, usually not out of sight of the truck stop.

I've had engines idling in severe conditions at 1500 - 1600 rpm trying to maintain 165º water temp.

 

Def build up in most cases is because cold air from outside gets in in that area of the exhaust system where it building up. There’s stainless steel gasket between def doser and dpf canister where it mounts, did you replace it. Can you post exact code the shop found out at the beginning when this problem started

 

Make sure your bellows tube between doser and the SCR is good. They leak at the connections and cause excessive DEF crystalizing

 

Can’t really understand the codes like 310CL, 3286CL, 3292CL. Maybe someone can chime in on those.
P20EE means SCR efficiency below 80%.
What’s the mileage on your truck??
They broke egr valve bolts and had to replace exhaust manifold, is that right??