I have replaced the old PC with a faster and the mode Sherline  doesn't work and a loss of step is had. Can I insert in step pulse and dir pulse a great value of 5 us to obviate to the problem directly? I use motor Sanyo and cards RTA planned to 800 step for turn. Do you think that I should reduce such value to 400 step for turn or secondary LPT to add a card to resolve the problem? Is there difference among a based PC on processor AMD and one on processor Intel?

Have you run a driver test on your new PC? Start there and see if you get a good driver test (flat line, no big spikes).