Probably getting close to a rebuild....
Growing up, vehicles in the 70s, at least the ones my family had, it was lucky to get 100K out of an automatic, especially any sort of work truck or vehicle used to tow with.
I put a drain plug in the pan of my 97's 5r55e, and it went close to 300K before things started to get go. Which was pretty astonishing for a first year 5r55e.... most of them blew out valve body gaskets and had other issues, it seemed. There were a ton of TSBs on that transmission in the early years.
Anyway, with the drain plug, it was easy to empty the pain (which generally got around 4 quarts out) every oil change, and refill. That put about a third of the fluid in 'fresh' at every oil change, and have no doubt that it greatly extended the life of it. Fluid was always bright pink. Once in a while, got around to putting in a filter, but can't say I was real diligent about it.
By the way, I've cut apart a tranny filter, and there isn't much too them. They really don't filter out anything but the biggest chunks. They can't filter out anywhere near to the level that an oil filter can, because there would be no way to keep enough fluid going through them for the transmission to work. If it doesn't have a magnet in the bottom of the pan, I'd sure put one in, once you get it all sorted out. Fluid levels are important. On the Ford transmissions I've dealt with, they did not like being down in fluid level AT ALL, especially in cold weather (97 5r55e and 96 Exploder 4r55e, I think).
A secondary filter, that cleaned up smaller particles, would be an interesting idea but don't think anyone has ever made one (like the secondary AMSOIL engine filters if those are still around).
Good luck.