I think this also came up in another thread. I think there are many variables which figure into cost of operation per mile, not the least of which is load, age on vehicle, driver habits, maintenance to specify a few. Unfortunately, it is not so clear as comparing fuel types though we are doing that. With two brand new trucks with no miles, for example, this statement regarding cost per mile may be true, though I have my doubts even then in every case. Even direct fuel for fuel, in the truck I currently drive the difference in fuel economy both loaded and unloaded with the price difference between regular unleaded and diesel between exact trucks aside from engine configuration or any mandatory modifications therein shows the diesel to still be more economical. Factor in the relatively small difference in cost of routine maintenance and the higher residual value, which is there but which I generally do not factor in due to its high variability, the diesel is still more economical in many applications, especially for folks who put a lot of miles in on their vehicles. Is this the case in each case? No. Is it the case in my case? Yes, at least on the vehicles that I am using/have used.
John M