I don't get how the occasionaly downshift can wear clutches and heat fluid...they engaged/disengaged on the way up the gears, and will do so as the car slows...they are all perfectly normal activities in the trans.
The clutches aren't doing (much) braking, the engine is.
Not suggesting that you should "row" an auto tranny, by any means.
I taught my partner to drive, partly in a 1978 Holden V-8 Auto (3 speed). Big (for Oz) car.
Coming into town, there is a "hill", that can take a Prius from dead "empty" to "full" about half way down (and the Prius keeps charging).
Brake smell at the bottom of the hill every time she drove, and I couldn't get her to pull "2" for the descents.
Put on my best Robert Duvall voice one day, and said that we were going to do the hill my way, then do it her way. My way was in "2", for her way, I would zip it.
When we hit the 60km/hr sign on the edge of town, she was to do a n emergency stop as 'though a kid had run on the road.
Did it my way, and stopped, and put a brick on the kerb.
Her way, and she was yelling as she tried to stop that the car wasn't stopping (it was, and it was stopping well, but there just wasn't as much available), and we pulled up maybe 20 feet further down the road.
We don't "row" our autos (and manuals), but DO select a gear that provides appropriate engine braking ability, especially on long grades.
As an aside, the vaccum modulator on that tranny went, and I discovered what I had previously read, that in the Holden Trimatics, they only apply the over-run band/clutch on 1st what "1" is selected.
On the way up, power is engine to diff, so there is no need for engine braking and they don't apply that clutch. Vaccum modulator gone, it wouldn't change to second in drive, but had no engine braking.