Have you considered to do some kind of current variator tweaking in a way, to do some discrete grinding here and there? Although scooters (and English language, for that matter) are not my cup of tea, I've heard (and saw) that some "Dremel" action, together with things you already did, do good on scooter's transmission.

An one more thing, that was recently confirmed for me one more time - for Chinese engines, heedful break-in is a must. Even doing nothing with the engine, after break-in period, you will sense the difference - it'll run smoother and cooler, be more agile, consume less fuel... Unless you kill the engine before that... So, I am convinced that after some 1500 miles, you too will sense that on your scoot.