prt alpha bad stutter

Hi
I just ran a v-carve file and it was cutting fine on the clearance part of the file but as soon as it started the actual 3d portion of the v-carve it started stuttering.
I slowed the speed down to see if that helped,but still the same
It was so bad it jumped a cog and ruined the piece
I am not hooked up to the internet
I have not changed anything for a long time as far as the computer or program and am running XP
Its been awhile since Ive done a v-carve but used to do alot of them with no issue.
Is this a communication issue?

THX
Brian

Forgot that I changed the Z axis to ball and screw.
Would a lag in the positioning of the Z axis cause the jerking with the x&y axis getting ahead of the Z-axis

THX