Great timing. I'm doing my own "100k" service. Last year was rough so it's getting the service at 115k. Doing the front shocks and since the cover is off, going to tackle the plugs. It looks like #8 will be the trouble maker. A mechanic friend thought that the heat shield on the firewall might be worth taking off. All I know is that nowhere in the ALLDATA site does it mention removal of the firewall heat shield. Only the inner fender cover.
New shocks on all 4 corners, new VLOM was necessary (broken 12v line = chaos and a $8000 dealer quote, fixed with $200 part and an evening of intake manifold removal). Have new Michelin LTX M/S2 tires last week. Brakes and fluids are for Wednesday then if I'm feeling lucky, transmission on Thursday. Wish me luck.
Winchester, can you take a picture of plugs even number plugs next to each other? With a good camera we might see a symptom. Also might try using a rubber hose as a listening scope to see if there plug is cross threaded. You should be able to tell if it is simply by the number of turns it took under no effort to thread in! Another trick is to use your cell phone as a macro camera to get in and take a closer look. I slipped my phone behind the engine to look at the flat 5-pin connector going to the VLOM when I was trying to diagnose my engine problem. That was hell and my phone let me see that it was unlikely a damaged external connector. Pulled intake and VLOM and probed the pins. No resistance going to the 12v line from any of the coil control lines! Didn't notice the damage for MONTHS because of the broken oil pressure sensor = disabled AFM if ECM doesn't know the oil pressure. Replaced the sensor, cleared the codes and boom, 2 min drive and won't accelerate over 40mph. Stalling and what not, very scary and all because of the terrible diagnostics routine for open circuit VLOM. That's another story. I'll let you know my tricks for cylinder 8 tomorrow.