2008 trailblazer, 4wd 4.2 i6, only had one code for a cylinder 2 misfire, replace coil pack and plug no fix misfire at idle and smoothed out while driving, shop said wasn't injector and they suspected intake valves. so earlier today i was undressing the engine getting ready to take the head off and i noticed that the marks on the cam sprockets do not line up with the dark links, the dark links are 1 tooth behind on both cam sprockets marks. wondering if any one knows some common reasons for this? bad chain? at this point it looks like i have to drop the pan for the timing cover and go through everything, right?