Getting +280,000 miles from a new 66RFE is actually a success, isn’t it?
Trans would have lasted longer if the guts of torque converter had not failed?

Logic would suggest: change the torque converter either at 250,000 miles or when periodic oil analysis shows a rapidly increasing concentration of “wear metals” in the ATF.

Always buy new, unused (never reman) torque converters and transmissions.
(meaning quality control is better at factories than at rebuild shops)

Start doing periodic oil analysis of ATF, engine lube oil and differential gear oil.
This analysis is an added cost, but not too different than paying $ for a “lifetime powertrain warranty.”
Both are a special type of insurance.
Throughout the mining, heavy machinery, transportation and military organizations - oil analysis is accepted as more benefit than cost.

My 46RH transmission died at 187,000 miles when the Torque Converter lockup clutch failed and sent debris through the transmission.
This happened after I changed out Mopar ATF+3 with added “Red Bottle” Lubegard
to straight Mopar ATF+4 with no Lubegard.

Maybe other Moparts members could comment on whether:
torque converter failure is the root cause more than 50% of the time in various model MOPAR automatic transmission failures?

In the late 1970s a company I was a supervisor at bought a Mack Midliner truck to make a 240 mile round trip five days a week.
This “made in France” truck went 1,000,000 miles by 1987 without a major breakdown.
The truck had a very good driver with a great work ethic who respected equipment.
Mack came and gave him a jacket with “million mile” emblems.

When someone said to me:
“So Charlie Babb has done such a good job looking after his truck that now you are going to “reward him” by making him keep driving it until it breaks, perhaps causing a road accident where he might get injured or dies? “

So even though money was extremely tight, I bought Charlie a new Mack Midliner.