I don't know if you found a solution to this - but I'll tell you mine all the same!
I had the same issue. CS Support wasn't really much help, but I found a comment on line suggesting that a faster PC fixed it for them. I was running a new i3 with 8GB 2GHz - so it isn't slow by any means. My servos (Fanuc with Ultra3000) were perfectly tuned & lightning fast. Running in test mode from the Ultra3000, or even a pulse generator they moved smoothly.
Connected to the CSMIO however, they were lumpy / jerky as hell. Looking at the scope in the U3000, I could see the step pulses were coming in erratically.
I tried it with a i7 16Gb 4GHz - and now the axis are smooth.
I fail to understand why a motion controller needs a fast PC. The jerkyness appeared even on straight line moves G0 Z500 kind of thing where I imagine the PC would just send one coordinate to the controller which would deliver the pulses at the required frequency. However, it appears to send continuously - maybe so you can stop in the middle of a move? It seems even more daft when the old PC with Mach3 & a parallel port BoB could drive them just fine.
The upshot is - if your servos are jerky, use a faster PC.