Unless you are towing a house gas is fine as far as power. Diesel's can rack up twice the mileage if cared for...but you give up some payload because the engine is heavier. So assuming both have been well maintained a gasser with 75000 and a diesel with 130K are pretty comparable. For me 25K is the most miles I'm willing to bite on. I go into some places where no one else is likely to come along for a week or two, and walking out 20+ miles is not on my bucket list, so reliability is paramount. The problem with used vehicles is that you never truly know how they have been treated and maintained, not for sure.