A904 issue with stock converter

Thank for the reply. I just put in a new 489 case that was supposedly rebuilt, everything looked new. It did it once with the old rear end and it seems to be intermittent. I replaced the filter and put the shift kit in after it sat for 20 years. Maybe the filter is gummed up, but the fluid looks very good. I'm thinking ill just tear it down and go through it since the condition is unknown.