i use penzoil 5w30 with fram oil filters. i used to use redline oil and k&n oil filter but that was getting way to expensive. so i now go the same way as JoeWagon, quantity over quality.
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If it has tits or tires it will give you problems, but atleast you can fix the problems with the tires
2007 Trailblazer - stock
97 GS-T -> lots of mods
98 GS ->total loss, now being parted out