Has it ever gotten fresh fluid? also it will generate more heat if your screen is getting clogged, they are cheap to replace but they are also reusable so you could just clean it. It wouldn't hurt it to have it flushed and filled with some Diamond SP and a new or cleaned screen. It's a cheap gamble compared to a transmission, worst case you have new fresh fluid and a filter which isn't a bad thing.

1999 Montero SAS'd on Kings and stuff

1998 Montero trying to get a V8 Swapped