So why would I want to upgrade my Turbo Diesel engine?
Better towing performance -- Maybe you bought your truck to tow that gooseneck for work, to get your 5th wheel to the next resort or the boat to the lake. It sure would be nice to get up to freeway speeds quickly and maintain highway speeds in hilly terrain. With the right upgrades, that can be done safely and efficiently.
Competition Use -- More and more enthusiasts are interested in heavily modifying their vehicles for competition use. Some are weekend warriors that use their vehicles during the week for routine duty then go to the track on the weekends while others are building strictly race vehicles that give up streetability for the demands of the track.
More fun -- For many, making modifications for increased performance is a way of personalizing the vehicle and to have a bit more fun with the daily drive. There is a satisfaction that comes from modifications that put you back into your seat a little harder when the light turns green. And, there are always the grudge matches at the local drag strip.