The VK56 5.6l V8 engine is sensitive to the quality of the fuel. The common problem associated with this is similar to the one on the VQ35 V6 engine. Bad fuel destroys catalyst converters on these engines, and that process accompanies by small production of dust and small pieces. The dust from the catalyst converters is absorbed by the engine, penetrates inside and grinds the cylinder walls, and then, washed by oil after that. This causes a rapid ware of all internal components (piston rings, cylinder walls, bearings). If it happened, well, you need a new engine. Symptoms of that disaster are the next: high oil consumption, loss of power, rough idle.
Timing chains are not reliable. In most cases, the right one is a weak spot. It stretches out sometimes even after only 30k miles. Aggressive driving with flour accelerations reduces the life of timing chains noticeable. The right chain also drives the high-pressure fuel pump, and in this case, the problem can be related to a failed pump. So, it is better changing timing chain along with high-pressure fuel pump, otherwise, it may happen again. By the way, the VK56 has a quite unreliable high-pressure fuel pump, which rarely goes more than 50,000-60,000 miles of mileage (80,000-90,000 km).
Besides that, keep an eye on the cooling system (radiator condition, level of coolant, and etc.), because the engine is inclined to overheat, especially the early models. They were equipped with unreliable AC condenser radiator cooling fan, which might jam and cause overheating. The engine suffers enough damage from overheating - twisted heads, blown head gaskets.
But in general, if you will keep it well maintained, use good quality parts, motor oil, and gas, the Nissan 5.6-liter engine last more than 250,000 miles (400,000 km).