She could still be a "GTP", you can slowly collect all the parts and mods you would need, install them one by one, then take a Friday off and use the 3 day to install the full top swap.
The tuning is computer reprogramming, the computer in our cars controls the engine AND transmission. Tuning will increase the performance of both, and is best to do with a laptop connected to the car itself, not just a "canned" tune from a company that mass produces them.
I think the trans tune you are referring to is the shift kit, it's fairly simple to do and will also preserve your transmission while making the shifts feel more solid and quick, not so much sluggish and meh.
There's other things that can be done, comfort, aesthetics, upgrades to certain systems, and the all important suspension and braking upgrades. Making the cat look good, feel good and handle corners like a boss is almost as rewarding as going fast. Lol
