clutch problem question any ideas?

[1988broncoll]

I checked the fluid for the clutch and it was black as hell like oil. So I went and bought some fluid and flushed the whole system till it came out clear down at the slave. It will start to build up a pedal but then it goes away. Right now I have it to where it has a little bit of a pedal but its not enough to get it to go into gear while its running. Before I bled it and changed the fluid I couldnt even get the gear shift to attempt to go into gear. Now it will start to go into gear but grinds and wont engage all the way. My other thing is If you watch in the resivor while someone is pumping the clutch it looks as if every now and then it blows the fliud back into the resivor like its building pressure then pushes back. I did the test on the master and the pedal got hard so im stumped. I dont want to pull the trans and swap the slave and then put it back togeather and have the same problem I am currently having. Any one have any idea as to what might be causing this. My buddy owned the truck for about 2 years and sold it 6-7 months ago and put a brand new clutch and slave in right before he sold it. I bought it from the kid that he sold it to and now this so I know the clutch componets in the trans are fairly new they might have 4k to 5k miles on them at most