What should you check before buying an LBZ Duramax?

An LBZ Duramax is desirable, but condition still wins. Check cold starts, injector balance rates if available, smoke, coolant pressure, oil leaks, fuel leaks, turbo behavior, and how the Allison shifts. Ask whether it has been tuned, how it was tuned, and whether supporting parts were added. A mild, documented setup is different from a hard-used truck with a vague tune. Rust is a big deal. Inspect frame rails, cab mounts, bed supports, brake lines, fuel lines, rocker panels, wheel arches, and the hitch area. These trucks are old enough that body and chassis condition can decide the whole purchase. Also check steering, front suspension, brakes, tires, service records, and towing history. If the seller wants LBZ money, the truck should have LBZ documentation and condition.