Several issues in play here.
Where do you live? If you are in a larger metro area, then you can probably find an independent trans shop that will install some or all of the upgraded available trans parts.
For example, Ford,Chrysler and GM all produce transmissions that go thru HUNDREDS of "factory" upgrades. They put this stuff out and redesign it as it fails.....WARRANTY....the stuff that dosen't fail MAY make it past the warranty coverage and they get lucky. What does fail is replaced with upgraded designs and sent out again....to be tested by the consumer again.
How long a factory transmission will last is simply a matter of luck.
Aftermarket trans specialists have redesigned and reengineered these same units, but the factory folks won't generally upgrade theirs due to costs. Bushings get redesigned with bearings, seals and o-rings are enlarged or doubled, pressure valves are opened up or restricted.....etc., etc., etc.,
Depending on the talent and attitude of an independent builder, you may NEVER have another trans problem.
There is no way that I would EVER buy a factory rebuild.
Find some guys that are into auto racing.....in any venue...and ask them.
Either way, transmissions are one of the best profit areas in the auto industry. On your worst day, you cannot generally destroy more than $400 in "hard" parts in a tranny and any tranny guy who cannot rebuild one in a day is lazy.....$3500 for the job is good money!
Now, I'll probably get some heat from some tranny monkey working for AAMCO, but I don't care.
I spent 18 years as a Service Manager for different big 3 dealerships, so I KNOW how it works.