The new-to-me 2008 Envoy is approaching 100,000 miles. I purchased it from the dealer who took in in trade. Original owner purchased from same dealer and has a history of regular service. I've done a visual inspection as well as I can of the plug wires and they look good. No misfires, codes or any telltale signs of plug failure. At this point don't plan to change out the Iridium tipped plugs at the recommended 100K. Anyone want to weigh in pro or con? Did the 100k tranny service drain, filter and fill. Fluid looks good. Anything else you would do at this mileage. Thanks for helping me out as I get familiar with the 5.3.