Laptops are not supported by ArtSoft unless using external pulsing devices and for good reason. That reason is the vast majority are very difficult to get Mach running right due to the power saving features in them, seems the more modern your laptop is the worse of a problem you are likely to have.
Disable all power saving features especially if you can find any in the BIOS but to be honest you will save yourself a lot of grief by going and buying a cheap second hand desktop and using that.
To give you an idea what you are fighting think about this, the time in int you reported is 20uS, when running at 45KHz the computer interupts at 22.2uS so your computer is using 20uS for pulsing and that is only leaving 2uS for everything else that is going on in Windows and Mach itself, I am amazed you have not had constant crashes.
Hood