deepgroove Z-axis

I'm setting up a deepgroove CNC kit with the 280oz steppers, the
deepgroove controller, and Mach3.

I am having some trouble with the Z-axis.

I've got the parallel port pins set up ok. The directions go the way I
expect.
I configured it at 32000 step/in and the travel seems to agree with the
Mach3 location measurements.
X and Y axis did fine at say 30in/min acceleration 4.

Z, not so much. I was running 5 in/min acceleration 0.5 and it's still
kinda dicey near the bottom of the travel. It's difficult to get it to
go up without skipping when it's near the bottom of the travel. Also
even mid-screw going up you lay a finger on it firmly and you can stall
it, not sure if that's "reliable". And 5in/sec is REALLY slow, but 10
is less reliable. At first I wanted to attribute that to the obvious
weight of the spindle head and motor since it seemed to be a going-up
problem, but in fact it won't go all the way down without getting stuck
either. About 3/4" from the table, going down, and it stalls out. With
the controlled off, I can tell it's harder to turn the knob in the up
direction than down as expected, but I don't feel a specific
obstruction or odd-feeling resistance. Couldn't really compare the feel
when it's at the "bottom" vs higher side-by-side because there's so many
turns between them.

I played with the freq, no real change.

Next I pulled the motor. It does go up and down freely now. The nut
can kiss the table. The head can go up and down at 30 in/min.

Is this a normal problem for the z-axis? What can I do about it? Is
there a break-in procedure I didn't find?

Danny