Chevrolet Repair: 1979 chev blazer 4/4, friction modifier, clutches

Question
transmission was slipping changed filter and fluid worked good for a while now when backing up it slips forward gears are good should i change the filter and fluid again and this time flush it.It was very dirty the first time

Answer
Hey,

 Could be clutches or band problem.  There is no external adjustments in that transmission.  Was the pan full of debris and clutch dust?  If it was it had to come from somewhere and that place was probably the clutch faces.  You could try adding a friction modifier like Lucas Trans fix to help it a long a bit longer.

Wayne