I did the full monty on mine at 178k. It didn't seem to change much except my trans temps were definitely lower. Shifting felt the same. My old fluid was pretty dark and had a slight burnt smell. Now it is nice and red. Gives me piece of mind since my truck is almost exclusively for towing.
I would maybe to a drain and refill and if it looks like total crap consider doing the "big job" (it wasn't actually bad).
The only thing i read to support NOT changing it is that the old fluid contains small particles of metal from wear and this actually helps with friction and engagement. I did experience this somewhat when i did a full change on my fx45 years ago. Transmission felt like it was slipping AFTER I did a full swap but that also could just be the computer needed to adjust to the new fluid and engagement. IDK
I would maybe to a drain and refill and if it looks like total crap consider doing the "big job" (it wasn't actually bad).
The only thing i read to support NOT changing it is that the old fluid contains small particles of metal from wear and this actually helps with friction and engagement. I did experience this somewhat when i did a full change on my fx45 years ago. Transmission felt like it was slipping AFTER I did a full swap but that also could just be the computer needed to adjust to the new fluid and engagement. IDK
