If you’re shopping a used diesel truck in 2026, “Cummins” isn’t just one engine — it’s a long-running diesel platform with multiple generation changes that affect towing feel, long-term ownership cost, and overall reliability.

The smartest way to buy a Ram diesel is to understand which Cummins generation you’re looking at, what changed year to year, and what ownership looks like depending on how you drive (highway miles vs short trips) and how you plan to use the truck (daily driving vs heavy towing).

This guide breaks down the major Cummins 6.7L generations, highlights what matters most for real-world ownership, and gives you a practical “best years to buy” view for the current used market.