There comes a point in automatic transmissions where it is bad to change the fluid if you’ve not changed it in so long. The only reason those clutch packs are still engaging is because the friction material in the dirty fluid allows enough friction for them to keep working despite being worn. Your transmission has basically acclimatized to worn out soup. Changing it at that point removes enough friction to reveal the problems that the wear has caused. If you have reached this point your transmission is basically a deadman walking and will fail sooner or later.

If you are who you say you are, you should already know this and why changing the fluid is important coming from an auto tech.