Cummins is the only option. The 5.9 liter six was designed from the get go for a life of 500k miles. This motor was introduced in 1984 and it's a proven design. 40% less moving parts inside than those off brand diesels. Have you ever seen a Powerjoke or a Duramax with 800k miles on them? There are even Cummins engines with over 1 million documented miles.