1999 Nissan Frontier

I am running a 1999 nissan frontier with a 4 cylinder engine with rw drive and overhead cams and such. It is your average manual 5 speed with basics and whatnot. I guess I just want it to be faster. I am looking for some things that I can do to get more power, more torque, and more horsepower? Any sugghestions?

can add a K&N air filter to pick up a few hp
can also change the rear gears for more top end speed or low end grunt
can change the cams and cam followers
header will free up a few HP
can also look into a performance JDM engine from one of the importers