It's really hard to say. If you have alot of miles on it and it has never been serviced it is kinda like rolling dice. When I bought my '87 GT it had 98K on it and I hav eno idea if the fluid had ever been changed. The pan was leaking though so it didn't matter I had to service it. The old fluid was still red and it has been three years now since servicing it and all is well. On the flip side of that however I had a Hyundai Excel one time that I decided to service the fluid in at 120K. The car made it another week before the tranny died. Now I have my '93 4 banger and even though the fluid is dark with 130K on it there is no way I will chance changing it out. I figure if it has made it this long and it is still shifting fine why tempt fate?
When I first got my car, the tranny fluid was nasty but the AOD would shift well. I changed the filter and fluid, after that the AOD would act up. When it was cold, it would hardy shift at all.