By black powder i mean ANYTHING black in the pan...That means on the magnet too, check the magnet for any type of build up. Most of the time it will be like a pasty silver or black build up. Also it might not hurt to just buy an overhaul kit for the tranny. Just if you don't know how the valve body works, dont take it off. Just unload the core and write down how it came out so you can replace the soft parts and slide everything right back in. Its really not that hard. Just a thought. You might also try to drop the pan and flush the tranny before you put a new filter on it. Just pour fluid into it without the pan on it and go through the gears while your doing it that might help reduce any build up that might be in there.