I am new to the forum and have been reading up on all the threads but wanted to validate, or not, my decision. I have a 2000 Chevy extended cab Z71 pickup that has 140k miles on it. I bought the truck in '01, with 10k on it, so have a complete maintenance history on it. It has had a Whipple SC kit on it since 65k, making 8 psi. The truck also has heads, cam, exhaust, diff, tranny, bigger injectors, etc, etc. No issues with the truck and it does not use or leak any oil at present. I have always used Mobil 1 10/40 but after reading up on this site I think I should probably change to 5/30, probably still use Mobil 1. I change the oil every 4-5k miles and my daily drive is fairly short - 8 miles each way, but I have 2 other vehicles so this truck only gets driven to work a couple days per week at most. I drive it mainly on the weekends when I am running errands, etc and try to drive it long enough to get the oil heated up good. I don't beat on the truck, but I do enjoy the feel of the power pushing me back into the seat, so I get on it routinely but not to excess. So should I change or stick with the oil that got me this far? Thanks!