Fixing your DPF Problems in a nutshell...

[Waterloo]

Any idea why that EGR Cooler failed? That is really odd...

Like Rawze asked, has the cooling system been pressurized to 20 psi to see it it holds pressure?

I would do a coolant exhaust gas leak test too, to see if you are getting exhaust gas in the coolant system. Napa has the Block Test Kits in stock, normally run around $50, worth the money.

The starter as Rawze stated...

Have you dropped the pan? I would pressurize the coolant system, let it sit overnight, drop the oil pan, bar the motor with someone underneath, a messy job, take a good flashlight with you. Bar the motor, make sure the area is quiet, turn off the radio, you are listening for gurgling in the head. Underneath, you are looking for coolant on the cylinder walls.

I would get the Block Test Kit and test the motor first, if it turns green on you, pressurize the coolant system and then drop the pan... It almost sound like a liner has slipped.

[Waterloo]

You said the DOC and DPF were serviced, were you there when they installed the cleaned and baked cans? Did you visually inspect before they installed? You said the truck is fine with the exhaust disconnected, I wonder if they did not do the work you think they did, and just through the old cans back in. That is a common practice nowadays in many shops, even the big name dealerships.

When the cans were replaced, was the ECM reset using Insite?