Axis Stall Problems

All:

My Sherline conversion is getting dangerously close to working,
but I'm running into some problems with axis stalling.

Hardware:
I am using an old Sherline lathe as my base, with vertical
milling column and a 13" inch table. Standard Shereline
CNC mounts are being used. I have 180 oz-in Sanyo-Denki
bi-polar stepper motors for each axis.

Electronics:
The electronics I designed myself. Here's a URL that
has the schematics and everything:

<http://gramlich.net/projects/cnc/motion/rev_d/index.html>

Basically, I use a venerable L298 with heatsink and eight
1N5822 (40PIV 3A Schottky Diodes) for each axis.

The power supply is 24VAC transformer, so the top voltage
is 34V.

The chopper is implemented using a dedicated Microchip
PIC16F676 microcontroller (one for each axis) running
at 20MHz where a couple of A/D lines are used to measure
the current flowing through each L298 H-Bridge. Each
axis is being sampled at approximately 20KHz. If the
current is too high, I turn the H-Bridge off and if
the current is too low, I turn it on.

Software:
I am running TurboCNC on FreeDOS. It is running on
1.1GHz Celeron processor.

The problem:
Each axis can turn slowly under TurboCNC, but after just
a little acceleration, the axis stalls. This could be
some sort of resonance issue, but I think it is more likely
to be problem with my chopper electronics.

I am currently using ripple drive (only 1 coil at a time)
in the stepper controller with a maximum current of 1 Amp
through each coil.

I have many options:

1) Increase the current to 2 amps.

2) Switch over to Full Step drive.

3) Switch over to Half Step drive

4) Switch over to Micro Step drive.

5) Find somebody who has a working system and
plug their controller into my steppers to
isolate whether it is my electroncis or
my mill.

Any suggestions on how to track this problem down and
rectify it would be greatly appreciated.

-Wayne