need ideas for my v6

I have a 1998 v6 mustang all stock with 98,000 miles on it, bought for 4400 it was a one owner car. Now i love the car but i hate the horsepower i really need some quick HP and i need some ideas besides the usual CAI, Throttle Body, i also looked into under drive pulleys and that looked promising but i just want to know what i should do first and what i should avoid... also in the future i might want to do an engine swap so what should i put in it... its also a 3.8