Before you start changing things, especially the intake, you might want to read this
http://www.duramax-diesel.com/spicer/index.htm
and here is the resulting thread
//heartlandowners.org/showthread.php/13313-Interesting-reading-draw-your-own-conclusions?highlight=
This was D/Max specific however you can probably find info on tests for your specific truck.
Unless you are going to use your truck (or any vechicle) for only one specific use, you might want to really weigh the advatages and disadvatages to any mod. There is a reason why they are designed the way they are. No matter what the application, one thing engineers have to build into any component is durability. In other words, the components are designed for minimal failure during a warranty period.
That may mean a compromise on power, mpg, rpm limits etc. but it is all done to protect the engine. Car manufacturers all would love to boast having the biggest baddest most monster truck out there, but they have to design and build them to conform to acceptable warranty failure rates, EPA standards, Cafe and a host of imposed guide lines. And then they have to please the customer.
That is not to say that there are not products that won't increase your performance, but it will be at some price down the road.