You can change your oil at any time. With not knowing the service history of your truck, I would change it now. Most people will tell you to change it every 5000-6000km (about 3000-4000miles). Some are meticulous about changing it at the mileage or every 3-4 months. If you stick to the mileage, you shouldn't have any problems.

Our trucks are also equipped with a light on the dash that will come on when it is time for a change. The computer bases engine oil wear based on your driving style and operating conditions of the engine.