The scren shots show your running Mach2, not Mach3. Its been a while sense I have worked with Mach but i was thinking Mach2 was limited to 25mhz pulse rate. It shows in your driver test that it is in 25mhz mode.
I know you can turn it up to like 45,000mhz and higher in Mach3. I am not sure about Mach2. I havnt set down and done the math to know for sure if this is whats holdin gyou back but it would be something to look into.