The old plug is Bosch double platinum bought at autozone, according to them was correct plug and gapped at .060. When pulled out it gaps at .065 after about 5 years. The new plug is ac delco iridium 41-101 gapped to .060 with feeler gauge. I'll check full pack tonite. I did notice damage to wires on 4 and 6, but after replacing plugs and wires on all cylinders little change. Engine is 3.8L non supercharged vin K. A couple of friends have pointed me towards clogged catalytic or flat lobe.Maybe its the picture but the gap seems excessive, are you using a wire gap gage?
The other thing is those are not the same type of plug, or again it's the picture, the one on the left has an extended center insulator compared to the one on the right. Use the correct AC-Delco plug for whichever engine you have 3.1 or 3.8.
Try swapping the coil for that cylinder with another to see if the P0306 goes away and you get a P030X.
Have you done a compression test?