I have a 2004 Tahoe with a 5.3 ltr. Flex engine, which has about 138,000 miles on it. I am not the original owner so I am not sure if the plugs were ever replaced at about 100,000 miles like it's supposed to. So I want to replace my plugs, even though I have no problems with the way the engine runs whatsoever. First of all shall I leave well enough alone or shall I do what the service schedule requires? If I do replace the plugs I want to give it the best I can in order to get the best performance and hopefully not have to do this again while I own the car. Here is what is currently in the car. The coil says:12558693, the spark plug cables are AC Delco #0745 and the plugs are AC Delco 41-985 - 12571164. Can I improve upon this or shall I replace the old with the same?