The only way you will get more power is a turbo, that or drop a v8 in it. They are a mechanical injection diesel, it's never going to be fast no matter what you spend on it without going for some form of forced induction, either turbo or supercharger.
In saying that, you could put extractors and an exhaust on it, but for that cost you could just about turbo it anyway and have a lot more gain than you would from just doing the exhaust...
Or you could drive around in low range all the time, lol. It won't give it more power, it will be a lot slower but it will feel like its got heaps of power, haha