There are really only three things you can alter in a diesel tune for performance. Timing, pressure and duration of the fueling events. With an electronic controlled engine, the potential is much higher and almost multiplies when some hard parts are added. Turbo back exhaust, fuel pump, cam, injectors turbo etc... (My memory is a little bit rusty on this and its cummins related so bare with me) I had stacked power adders. I had a TST performance chip stacked with an edge juice with attitude tuner. I had stock fueling so I really couldn't get the full benefit out of the combo but I had ALOT of adjustment with them. The TST chip had a selector knob that let you go from 0%-100% by twisting it. IIRC it was a pressure box. The edge juice modified the duration of the fueling events and let me set my transmission (auto vs standard) my alert points, and several other things that I can't remember off hand. I really liked just cracking them open a little bit each because it was hard to keep the temps down on a long hard pull. The pressure box was great for the low end and the tuner worked better on the top end.
Either way, if you have an auto, look out! They don't generally hold up well to performance tunes. Also, cooling becomes critical as well as making sure you have safe pyro temps. This should be inserted pre turbo for a better idea of what the motor is putting out and more importantly what the turbo is being subjected to. If you have a stock clutch, I'd be leery of running much more than a few hp over a stock tune. I ran a dual disk south bend clutch and never had an issue holding the power. (A mouse built a home in it one time and that smoked it one time). The chips are a lot milder than the tuners and there is not a possibility of your ecm code being destroyed.
