What should you check before buying a used 5.9 Cummins?

The 5.9 Cummins has a strong reputation, but do not let that distract you from the rest of the truck. Check cold starts, blow-by, oil leaks, fuel leaks, coolant condition, turbo noise, injector history, lift pump history, and any signs of hard tuning. If it is a 24-valve truck, ask about fuel pressure and lift pump support. The transmission matters. Many automatic trucks have lived hard lives. Test shifts cold and warm, light throttle and under load. Look for slipping, flare, delayed engagement, or harsh shifts. Then inspect the front end, steering, suspension, brakes, frame, cab mounts, bed, and rust. Older Ram trucks can need a lot around the engine. A clean, documented 5.9 is worth attention. A neglected one should not get a pass just because it says Cummins.