Hello!
I have a problem with trajectory distortions on my new router(under Mach3 indeed).
I tried to mill simple 45 degrees raster, and get unexpected result
Look at these photos. Feed on first photo 1000mm/min, on second - 10000mm/min
I'm think that reason is a acceleration patterns inconsistency between X and Y.
What can i do?

It looks to me (without having seen your machine) that you're running into backlash.

No, i removed all backlashes for sure
Machine -
http://www.qilicnc.net/producthtml/200.html
but with fully replaced control ( nice kit! )
I forget to say that this raster 100x100mm size, so that the error exceeds 2mm!
My instance of machine is powered by Yaskawa servodrivers. May be problem is in servos, and they reaction on pulsetrain((

It would seem to be your servo tuning is the issue, as you suspect.
Hood

I can't imagine what exactly was а source of problem, but i fix it.
Thank god, servodriver has pulse filtering function, which brings time delay in input pulsetrain.
When i added some delay in Y axis pulses, lines in trajectory become straight.

Not really sure what setting that may be but as long as its working thats all that matters
Hood