1988 B350 Van trannsmission issue.. Help

[csf1975]

I have a 88 b350 with a 3speed automatic trannsmission , and I'm having a few issues with..
for starters Here is what has happend. It was starting to slip, so I changed the fluid and filter.. the fluid was black as coal, It fixed the slipping problem but now, after driving it shifts ok, But going 50 mph and if you let off the gas it starts to down shift and it pulsates.. Also the fluid is almost black again.. after 50 miles on a filter change.. Any tips would be greatful.. I plan on doing a flush this weekend and hopefully it will fix the problem..

[Chump]

Flush the tranny and change the filter again until you get pink fluid running thru it. You might be a little late and may need a rebuild?

[csf1975]

well I did a Flush and new filter.. drove her for over 200 miles, and it did great.. no problems with shifting.. I had to disable the Kick down cable, it was causing some problems. I tried everything to adjust it, but could not get it. Once it was unhooked it ran fine , just did'nt have passing gear.. unless I manual shifted to second gear.. I will work with it moe.. I will do another flush in a week or so.