My 3 axis CNC works fine with Mach3. I had a 3 axis USB movement card and I have changed it to a standard 5 axis BOB as I thought there was a problem with the first board. But It still exists.
 If I load a large Gcode into Mach3, when I try to toggle the axis or zoom in on Mach3's graphic table display, the stepper motors slow down steps to almost individual steps. I ran a latency test on my PC, which the results were good. ( servo / max int 1011675, max jitter 15071  // Base max int 42076 // max jitter 19317 )

Any Ideas Please ?

Note .
 
 This only happens with large Gcodes loaded into Mach3

I have tried changing Kernel speeds. Maybe not enough video Ram in the PC ??

Anyone ?

Not much help really but...
It sounds like your video card ram is insufficient - try disabling the toolpath display (diagnostics screen) if everything then runs fine then that should be the proof you need.

Tweakie.