Transmission Filter (external)

As an attempt to fix a Trasmission on a '91 Legacy that slips once the engine has warmed up I bought & installed a new external transmission filter. However, i didn't pay attention to what hoses went into the "IN" & "OUT" side of the filter. Does "IN" mean from the transmission or from the transmission cooler? I'd think from the transmission but I want to make sure. Does anyone out there know for sure??? Thanks.

I think I might try replacing the internal filter again as maybe its clogged. The external filter was pretty dirty. Could it be possible that the trans cooler is clogged?