J Cronnelly:
There are now 4" exhausts for these trucks I believe, install one. Install pyrometer/boost gauge, change turbo or the exhaust housing(anyone between 12cm-16cm), different air intake system, install bigger injectors (mine came from ADT and were VERY good) but there are many others, last it is time to tweak the pump. More fuel, low end boost, timing, governor adjustment, and many other custom parts. You can also read the post on up (Sticky) that says:"Stage1, 2, 3... ) as this will tell you how much you can do and maybe estimated horsepower.
Hope this helps.
John