Looking for any input from you die hard GMC folks like me. Just found a great 2003 Silverado , one owner with low miles. Would like to know more about the Vortec engine and was looking for possible websites that you could pass along. It has been recommended to me that I start using Synthetic Oil. Never have before. Looking for any advice on the subject. I plan on keeping this and driving the wheels off of it so engine longevity is important to me. Any technical info that is out there on this particular truck, the 5.3 Vortec and the Synthetic oils I would very much appreciate it. Thanks.