KSHall,
The AFE intakes are one of the best available, but do NOT buy it for HP, they do make HP but the reason to get it is to lower EGT's and help to quicken the spool up on the turbo. The Pro Guard 7 is also something you should consider very strongly, it's the one filter media thet allows tons of cold air thru but stops the dirt. The typical 4 layer gauze filter just lets in waaaaay to much dirt on a diesel engine, on a gasser they are OK, but on a diesel they just aren't up to the job etc. You also have options with AFE a Stage I or Stage II if you really plan strong HP mods the Stage II flows more air and sounds way strong too. Think about what you plan to do and then pick a "Stage" in Pro Guard 7.
Mark @ DPPI