I Lost owners manual long ago and I'm wondering what the power button is supposed to do.I don't notice much difference when it's activated.When I had bosh plugs instead of denso it seemed to have more kick.

It will more the shift points up a bit. Good for towing.

It makes the transmission shift differently. It will shift to the next gear a bit later, giving you more power for pulling or accelerating. It will also down shift sooner when you go to pass someone so you don't have to matt the throttle pedal to get it to downshift.