Just a quick suggestion, if it ran better before it was tuned up, than it was something that was done when it was tuned up, open the hood and look around carefully for a vacuum hose that was left off, around the throttle body area, under the air cleaner etc.. make sure all the hose connections are tight by feeling them with your hands. look for loose clamps. Countless numbers of times i find these problems on customers cars. People rush to get work done and these things get missed. Other option, take it back to whoever tuned it. I'm sure if you look hard enough, you will find the problem. Please rate this as helpful, if it was, it is the only way to improve the service.
A 2001 is difficult to power-up. Depending on your budget I would do a high flow intake and exaust. If it is an LPT you can always put in a bigger turbo with a higher flow. If it is an LPT look for a turbo beginning TD014. The next numbers are the different performances e.g. 18T 19T. After that get a custom tune flashed into your computer. If it is an LPT, a 19T with these mods can increase the power to almost 300hp.