Black/dark fluid is a bad sign. Personally, rather
then draining the pan 4 or 5 times, I
prefer the "let the tranny pump do the
work" method.
Disconnect the upper transmission line
from the radiator. Push a 4-5 foot length
of hose onto the fitting on the radiator
and drop the other end in a 5 gallon
bucket.
Tips: A length of old 5/8" garden hose
works for this. Use a worm clamp to hold
the hose on the fitting. Trust me, you
don't want this coming loose. Place a 3"
C- clamp or some other contraption on
the rim of the bucket to hold the end of
the hose a couple inches inside the top of
the bucket. Again, you don't want this
coming loose.
Stick a decent sized funnel in the fill tube
for the tranny and arm yourself with 8-10
quarts of the proper ATF. Now you need a
helper.
Have the helper start the engine and
keep their foot on the brake. As soon as
they do, your old black fluid will start
coming out of the hose into the bucket.
Your job is to pour new fluid down the fill
hole at the same rate its coming out of
the hose. Don't worry about being exact,
just keep the funnel full. Keep watch of
the fluid going into the bucket. It should
start looking better. After your first
gallon, have your friend, with e-brake and
foot brake both applied, shift through the
full range of gears, stopping for about a 4
count at each spot. Once he's at the
bottom, he can put it in Park for the rest
of the process. When you see nice red
fluid coming out of the hose, stop filling
the funnel and let it empty. About 5
seconds after it does, have your friend kill
the engine.
Hook everything back up. You've just
done a complete, or nearly complete
change of your fluid, including all that sits
in the torque converter! This method is a
" forward flush" as apposed to a "reverse
flush" that many shops do. The forward
flush is far less likely to damage all the
seals in the tranny and is gentler on
things as it uses the tranny's own pump
and normal operating pressures to do the
flush!
Once you're done and everything is
buttoned up, take it for about a 15 mile
drive to get everything up to full hot.

Check and top off your fluid as necessary. This method is also done all top side, so its easier to stay clean, doesn't require crawling under there on your back, or trying to change all the fluid 3 quarts at a time by draining the pan multiple times.