I'm just about to hit 100,000 miles in my '99 and am wanting to do some maintenance and replacement of a few parts.
1) what are the pro's and con's of the expensive spark plugs and wires? Is it worth the $10 each for high end one, or are stock Delco ones just as good?
2) I keep hearing good and bad things about synthetic differential and transfer case fluids on older vehicles, such as mine. What is your input and thoughts on the topic?
3) I generally keep pretty up to date with maintenance, so nothing on the truck is broken or at the limit of its lifespan, but what else should one change out at the 100,000 mile marker?

I am welcome to any input or suggestions. Thank in advance everyone!