Can a slipping tranny be fixed by changing the fluid? 05 ford taurus has 135,000 miles and never changed the fluid.it is used to deliver the mail

It would be a band aid, It might help for a little bit but it sure won't fix the problem.

The clutch packs are likely shot. You can give it a try and see if it helps. This write-up may help:

https://www.askmehelpdesk.com/cars-trucks/faq-how-troubleshoot-repair-maintain-hondas-selected-other-vehicles-46563-5.html#post552241

ATXs are the weak link in all FWD vehicles. Ford recommends dropping and cleaning the pan, replacing the filter, and chaning the fluid every 30,000 miles with Mercon V. I use Mobil 1 Synthetic Multi-Vehicle ATF, for an extra margin of safety, and still change it every 30,000 miles on my 2000 Taurus. The ATX should go the distance, following this procedure.

It would be a band aid, It might help for a little bit but it sure won't fix the problem.

Changing fluid my make it worse at this time of trans. Life, it would clean out the "pot holes" in the tooth flanks and increase the wear and act as a hydraulic pumping action on the worn flanks. And weaken the tooth profiles. Problem is in your clutch pumps..