Car sputtering and stalling out while driving?

I've owned a 96 Jeep Grand
Cherokee for a little over a year now.
The problem started a few months
after I bought it. Basically, the car
just sputters and shuts off in the
middle of driving. Sometimes it
backfires. It started off with just
shutting off with no warning or
sputtering every few weeks or so and
starting right back up again, but it
has advanced far past that. For
about two weeks straight, I couldn't
even get five miles without it stalling
out three or four times and taking
three to five minutes to start back up.
My father, who is an electrical
engineer, saudered my PCM in a way
that eased the problem for about
four weeks with no stalls. It has now
come back much worse, hardly
making it half a mile without
sputtering and stalling. It's had a full
tune up, the timing is set right, I
replaced the cap and rotor,
supposedly gotten any air or water
out of the fuel line, I even replaced
the O2 sensor and ignition coil. I
can't drive this car anywhere without
fear of getting in an accident. Any
ideas?