First my set up:
Toshiba Laptop with XP and a built in parallel port.
4 Axis HobbyCNC (only running 3 axis)
305 oz motors on a Widget Master table (8" by 8" working area)
Spindle is a Dremel with a 1/16" end mill bit

I have Mach3 with Motor Tuning at:
8000 Steps per inch 33.708 Velocity and 1.5 in/sec/sec Acceleration.

At these settings the motors run very nicely, not too fast as the table is small and I'm not in a rush.

Problem:
The cuts I want to make are quite complex (gear teeth) and accuracy all the way through to the end is imperative. By feeding in g0x2 I get good results and it is reproducible. However when I put in the gCode for a complete gear one or another motor will stall (not always the same one) and the DRO's keep going while the motor makes a really ugly vibrating sound, so the cut is destroyed, at times ending in a blue death screen.

I have a hunch its the computer doing something in the background that is messing things up. I have turned off the wireless but what else and how do I disable or turn off other interference.