When performance and torque control are your objectives, there's little doubt that a manual tranny is the way to go. If I had a magic wand, I'd make my cars auto tranny into a 5 speed, for sure.
However, there is absolutely no evidence to support claims that "4EAT’s are pretty weak after ~140k". Dunno where that came from, but it's pretty bogus. It's true that due to the nature and construction of an automatic transmission (i.e, more moving parts, more heat, etc), that it'll eventually fail before a manual tranny, but if you provide regular maintainence, and don't drive around specifically
trying to roast your transmission, a 4EAT will provide you with years, and years of service.
One of this boards best contributers, who is now, sadly gone (*salute Ciper*

) was a very big proponent of the 4EAT, in fact.
I'm not suggesting that auto's are better, or more durable beyond 200k or anything inflated like that, but that with regular service and a reasonably conservative foot and driving habits, an auto tranny is almost as good as a manual transmission in terms of longevity.
Getting back to the original post, however, I'll repeat my earlier suggestion based on your latest offering: flush and refill the tranny fluid with a high quality automatic transmission fluid (I'd suggest synthetic if for no other reason that it'll allow your tranny to operate a few degrees cooler). Also, consider installing a tranny cooler -they're cheap and can extend the life of your auto exponentially.
I've heard the following phrase on this board a number of times, so I'll repeat it: "If it ain't broke, don't fix it".
Seems like pretty sound advice to me.