Thanks for the reply BigTruckDriver

I currently have the stock exhaust system on my truck. A good system, but things can always be made a little better.

A good friend of mine is a Nissan Tech and he has the tools to re-flash the computer after any modifications are made. There is a code you can send to the truck's ECU that brings everything back to factory settings (before the truck leaves the factory) and the ECU re-learns the truck and treats any modifications like they came stock on the truck. Essentially making the best out of any modifications you make

No ideas on the muffler sizing?