You need to let her breathe in and out better - she's constricted from the factory on both intake and output.
You will get marginal sound increase with new muffler, but not much more breathability unless you cut the hydrocarbon filter out of the upper part of the airbox and utilize the CAI design put there by the Yota engineers. Then change the headers out along with the Y-pipe. It's like an audio system - it can only sh*t out what it eats.
This won't pass any emission station, but the 4.7 no longer has asthma. Here is what she sounds like opened up - and it drives like a completely different truck.
http://https://youtube.com/shorts/e54plBbOlaQ
To bring it all together and truly complete the transformation, get the YotaWerx tune. Those guys are as professional as it gets.