I have a homemade 3 axis router with Probotix electronics.  Mach3 is loaded on an older Windows XP machine.  When the motors are jogged with the Mach3 jog flyout screen,  the motors move smoothly and continuously.  The same thing happens when using the Mach3 motor tuning screen.  However,  when the motors are moved with G Code instructions (with the G0 or G1 commands), they move approximately .3 inches, pause momentarily  and then start moving again.  The motors repeat the .3 inch movement over the entire length of the G Code move.  This happens on all three axis.  To the extent it makes a difference, the machine uses single start Acme 1/2-10 lead screws on the X and Y axis.   
 
The machine does a nice job cutting.  However  am hoping someone can offer some advice with respect to getting the motors to run on a continues basis rather than in .3 inch pulses.

Close Mach and go to the Mach3 folder and double click the drivertest.exe and let it run. See if the line in the graph is smooth with no spikes.

What kernel do you have set in Mach?
What is the Time in Int on the Diagnostics page, also the frequency?
Do you have onboard graphics card?
Do you have QuickTime installed?
Hood

Thanks, I will check those settings tonight.

Also try turning off the toolpath display. The on/off button is on the diagnostics page.

Close Mach and go to the Mach3 folder and double click the drivertest.exe and let it run. See if the line in the graph is smooth with no spikes.

What kernel do you have set in Mach?
What is the Time in Int on the Diagnostics page, also the frequency?
Do you have onboard graphics card?
Do you have QuickTime installed?
Hood

The graph generated by dirvertest.exe  has multiple spikes.

The kernel speed is 2500hz
The Time in Int is between 6.8 and 8
The frequency is 25387

I do have an on board graphics card.
I just uninstalled QuickTime.

Ok run the driver test again and see what its like after uninstaling Quick Time.
Onboard graphics can be problematic when using the parallel port.
Hood