Ford says fluid in PTU will last the life time of the vehicle. I donor believe that be true because all fluids need to be changed at some point.
You're not alone. It's 75w-140. People in the know appear to be changing the fluid every 25-45k. They say it turns to sludge about then... gear oil/atf should not be too thin (won't dissipate heat effectively) or too thick (won't fill in every nook & cranny effectively), like is happening to these PTU's with "lifetime" claims about the oil. Laughable. Here's a really good writeup about a Ford Flex, I can't speak to the Taurus, and couldn't find much on it using duckduckgo.com search engine, there might be something on video sharing websites specifically for your model...: at the fordlex.net forums
From that write up, his third post, the "Results" after the job was done:
So far I've just taken a quick ride and driven about 20 miles to see if I could "feel" any differences. Almost immediately, I noticed that the vehicle seems to have less drive train drag. For example, when I am heading down a hilly road that I have driven hundreds of times before, the car feels like it is able to coast faster/better than before. I am not having to step on the gas as much to maintain speed. I jumped on the highway and noticed that low RPM throttle response felt better. What I mean is that cruising in 6th gear at 60mph and modulating the pedal resulted in much more of a feeling of acceleration and response than before.
That's just the highlights...
That write up is referenced here with a two separate reports from someone who tried it on another forum including his tips and explanation of that first link (always such a great resource to see what happened when someone else followed a write-up), scroll down to Reply #6 for those two reports, since I included that whole thread because there is some good discussion there I think: ecoboostperformanceforum.com
You have to be a member and logged in to search that forum btw.
I would say, many vehicles seem to have transmission related failures if they were kept in good condition otherwise, with high enough mileage. Therefore, the best things to change of course are the engine oil, and transmission components' various oils.
Honda changed their transmission fluid around 2009/2010 I think, roughly. But it didn't matter, they were still telling people not to bother replacing the ATF in their Accords or Fits (personal examples) until 100k... even with the old inferior ATF inside them... that's a pretty clear tipping of them on their part. They're happy to sell you a new car if there should be something wrong with your current one though, we shouldn't worry about that... ugh...
This scam is well documented in tons of forums for all manner of brands and models of vehicle. I'm glad you asked the question. Hope the answer serves you well.