Hey John,
Alright so I loaded up your PWM setting into MACH3 and found that you're running at 100Hz, which is fine. So now we need to get MACH4 to replicate that. So I would take the following steps to ensure your setup is correct in MACH4.
1: Configure > Plugins > UC100
2: Set the Spindle frequency to 100
Now we know the correct frequency is chosen we can make sure the MACH4 spindle parameters are correct.
1: (still in MACH4) Configure > Control > *Top right hand corner of dialog box* hit the right arrow until you see the spindle tab. Then click it.
2: Once at the spindle tab set your max RPM to the RPM you had set in the MACH3 for your spindle pulleys. (MACH3 > Config > Spindle Pulleys.)
This way we know we're working apples to apples.
Once you do this you should be in working order, however I know this can be troublesome so if you don't get it right away let me know and we'll find out where you went wrong.
The pulse width is based upon the maximum RPM the spindle is allowed.
If screenshots would help just ask and I'll post them up for you.