My only issue regarding all your effort is that i would've personally done one thing at a time then tested it.
The fact you are none the wiser leaves you a little bit open, as you can't pinpoint anything!
If the air filter doesn't sort it out then my next move would be a proper tune up place with a dyno.
It ain't cheap, trust me i know all too well, but it sorts things out, just be polite and ask them nicely exactly what they're doing!
I dunno what area you're in, but the fella that does mine walks into the waiting room with half my bike on his lap and narrates to me why and what he's gonna do next!
As much as i hate the end price, the bike says differently!
I use PDQ in Taplow, well out of my way, but i can safely say he's like a bike surgeon!
