I have a 05 Duramax and I want to improve my MPG and get a HP increase. What I am looking at doing is staying with the stock air intake system with a K&N drop in filter and stock pipe with an Aero 3535 muffler. I want to install an Edge juice with attitude. Are there any problems with this? When installing the muffler will i need to replace the pipe or will it be a simple swap with the stock muffler? What about going up to a 4" pipe will that be better than stock? Any advice is appreciated, I just want to keep my truck reliable and at the same time get a little more power. thanks for any advice.