The right answer completely depends on what you are using the truck for. Initial purchase4 price, trade in values, gas vs diesel prices, fuel mileage, resale value, maintenance costs, tire life, and all the other stuff that gets harped on endlessly, have never been the salient factors. It was always, and remains, what was the best tool for the job.
I am really good with numbers, I can prove easily either side of the argument with just a few changes here and there. A simple example, I invest the 10,000 difference in the diesel cost at 8%, which doubles in value to $20,000 in 9 years, and I can easily bend the outcome.
None of that however, will make a 6.4 the right answer for pulling 20,000 pounds through the mountains daily. It also won't prove the diesel is a great daily driver choice for a 6 mile commute.
Outside of the right tool for the job, the rest of the reasons for making this choice are basically indefensible, and they don't need to be. If you want a diesel just because you do, then all the math in the world shouldn't stop you. I have wasted way more money on far more frivolous stuff than pickups. Best of luck.