How many miles can a 5.9 Cummins last?

A 5.9 Cummins can run very high mileage when it has been serviced correctly, but the engine is only one part of the truck. A high-mileage Ram can still be worth buying if it has records, clean starts, controlled blow-by, stable temperatures, good oil pressure behavior, no major leaks, and a transmission that shifts cleanly under load. The risk usually comes from the rest of the truck: automatic transmission wear, front-end components, rust, cooling issues, wiring age, neglected fuel-system service, and hard towing use. Treat mileage as a pricing tool, not a pass/fail rule. A documented 250,000-mile truck can be stronger than a lower-mileage truck with missing records and obvious neglect.