I have only had my new AM-3 out for a grand total of two nights but it is already looking good.
On the first night using fairly generic guide parameters except for a 1sec guide exposure I have to admit that the results were less than inspiring (see first graph below). Then I found an extremely long (you will need a few hours to digest it) but highly informative thread on how to optimise guiding of harmonic mounts:
https://bbs.zwoastro.com/d/15989-get...from-my-am5/15
I have so far only implemented a couple of the suggestions in that thread (guide exposure down to 0.5 sec and max durations down to 150ms, with very low aggression) and I am already seeing much better guiding (see second graph below).
Clearly there is still periodic drift in there (both these sessions are three hours long) but there is also still plenty of room for further mods including upping the gain on the guide camera and playing with the sidereal guide rate. The latter is set as 0.5 by default in the ASIAir but people are suggesting improvements can be made by using a lower rate again. I believe the next update of ASIAir software will allow this, currently only the ASI Mount software allows it.
I would highly recommend reading at least parts of the quoted thread if you have an AM-3/AM-5. It really helps you to realise that every single mount has quite different characteristics and so guide settings need to be individually tailored.