Fbody brakes will work on 04+ Grand Prix's. Some have even converted to Corvette or CTS-V brakes.
As far as I know the 06GT is tuneable. I'm unsure on the older pcm question.
97-03 struts should work on 04+ GP's. They are basically the same car with a different body. Not much has changed. I have 2004+ exhaust on my 99 that I only had to cut one exhaust hanger off to make it fit. They changed a placement of one hanger that's it.
Do read up some more but your questions were not that bad. I've seen worse like "i want a fast car" or something totally generic.
These cars are getting old and cheap. A lot of dummies will come on here and just ask really ridiculous things.
Feel free to ask more questions, this is your thread to do it in
