Don't believe the factory saying they'll last 100K.
Dump them ASAP, and don't get fancy, replace them with the exact same
You'll get a bit of sticker shock when you go to buy the AC Delco Plugs,
but have peace of mind knowing that a good running vehicle right now is
very good thing to have.
A few tips to remember, if you can, blow away any dirt/dust away from
where the spark plugs sit, be careful on the wire/boot removal twisting
them rotationally before trying to yank them, (A plastic Boot Puller is
of help sometimes) double check the proper gap, and don't torque them
in like a gorilla.
Yep, you might need swivel extensions in varying lengths, and the
proper size spark plug socket. Do the changeout with the engine cold.