Hi Fred,
If you are running Mach3 in Demo mode then it is limited to 25kHz.
It is generally best to run at the lowest possible Kernel speed that still allows stepper motors to reach their full speed (if Motor Tuning will not allow motors to be set at a higher Velocity then the Kernel speed has to be increased). It is unfortunately a human failing that we want to run Mach3 at the fastest possible Kernel speed, thinking it will give better performance, but that is false.
I know it is just a typo but would your PC run at 35000 mhz ?
Tweakie.