Having worked for and retired from a Heavy truck dealership and private fleet owner for over 30 years, I got to watch first hand the progression of diesel engines from basically no emissions controls to what they have today and the costs associated with maintenance.
My primary motivator for keeping my 1997 no emissions pickup truck (other than it's a classic OBS 4 door 4x4 long bed). Today's diesel engines, in order to meet the Tier 4 final emission mandate have become very complex, totally electronically controlled and because they are and because most of the components are lowest bidder sourced, I don't want one. If something happened to my '97 and I had to purchase a new truck, it would be a gasoline motor, not a diesel because gasoline engines with emissions components have had time to be perfected and reliable whereas the Tier 4 final diesels are not.
Fully 85% of the shop work on 2013 and newer diesel trucks is emissions related issues and most of those issues pertain to failed components and failed electronics, not the mechanics of the engines themselves.
Additionally, a the added cost of a Tier 4 emissions compliant Class 6-8 truck is around 20 grand per unit.
Having said that, I'm quite comfortable not adding urea as well as diesel fuel to my tanks and I'm quite happy with not having the big power that I don't need anyway but I'm especially happy about not having the complexities associated with a Tier4 final diesel engine.
A new comparably equipped truck to the one I own would cost me 3 times what I paid new for mine. I cannot see any justification in a price thats 3 times what I paid in 1997. The cost versus technology versus reliability to pan out for me.