Just a couple things,
When we sold our 2001 Ram 2500 with 315,000 miles, I got just shy of $10,000 for it. We had bought it eight years earlier for $14,000 with 234,000 miles. So for a 18 year old truck with 314,000 miles don't think that is too bad.
A gasser would have gotten maybe $1,500.
The rest is just choice, yes maintenance is more, not going to break the bank more just a bit more.
What surprises me is the number of diesel TV we see coming into the park towing pulling TT that come in way under 10,000#. They don't need the diesel, they buy it for ease of towing.