/6 904 transmission swap still having problems....

Your original trans. had a burned up front clutch pack or bad seals in it. Either way it wasn't working properly.

Even though you replaced the converter with a new one 3 months ago you ran it in a bad trans. that most likely filled it with clutch pack garbage. You should never use a converter from a bad trans. in a good one unless you have it professionaly flushed out. I'd drop the pan and see if the filter is plugged. It's possible all the garbage from the converter plugged the filter. If it's not that it's what TB said which is the new trans. has hardened seals and if it hasn't been rebuilt it wouldn't surprise me. Remember, the last 904 was made well over 20 yrs. ago so it's nearly impossible to find a good used one unless it's been rebuilt.