Another thing I tried to test the weight of the head was upped my accel to 2" per sec, raide the head to 7" above the table, with 0" set at 1" above the table and z-axis speed of 100 inches per minute.  I did a G0 Z0 and it was exactly 1" above the table so it stopped the axis no problem.  If I repeat it over and over I gradually lose it though.

Here is a pic of my z-axis as requested. 


I no longer seem to be having that issue with height so I do believe it was solved.  Just ran through all the tests and so far so good.  However, I did have Mach 3 just stop responding and would show me "Server Not Responding" with Switch To and Retry options.  No matter what I did I couldn't close out.  Even through Task Manager I couldn't close out.  It takes a full reboot to get back up and running. 

I no longer seem to be having that issue with height so I do believe it was solved.
What solved it?
Did you try reducing the velocity? At what velocity does it skip?
Have curve for your motor?
What kind of drives are you using?
Post your xml and will maybe someone will have a look.
RICH

I'll grab the XML tomorrow when I go back out to the shop.  I switched from the on board parallel port to a PCI parallel port.  Seems to be working now.  I had tried reducing the velocity from 1"/sec to .25"/sec.  Didn't make a difference.  I was the exact same amount off.  I'm using Nema 23 425oz drives.  I have played around a bit and bumped up my accel to 2"/sec and don't seem to have any issues with that either. 

The 3.3v PP can create problems along with on-board graphics. Most, but not all PP cards ,that you buy are dual voltage and you want to use 5.5v.
That may well be your culprit.
RICH