[Sienile]

That's code for Jeepman doesn't like NGK's warranty. Champions are fine, but NGK iridiums are a little bit better.

 

[Sienile]

It depends more on miles and idle time than age. NGK won't really affect performance in the short term, but towards the end of their life. Their electrodes don't wear down as fast as the stock Champions.

 

[Sienile]

The loss of power is likely delayed VVT actuation. Exhaust phasers tend to be the first to have issues. You might notice a rattle on start-up sometimes when they first start going bad.

There is no difference from brand to brand in the tuning. Export models have a higher speed limiter, but that's it.