On my 21 I swapped out just the muffler with a black widow mid aggressive muffler, I love the deep sound it gives not to loud on cold start but when u get on it u could hear it, mild drone at highway speeds and the cylinder deactivation isn’t that bad for me, but then again I really don’t hear...
I have a 21 and mine opened going down the highway I was able to pull over safely and close it, the prior night I was emptying out my catch can so maybe it didn’t close right.
I have always used 87 octane from Costco with no problems and one day I filled up with 91 octane from Arco and my engine starting knocking I have a 5.0