[bertram928]

If I was Toyota I would insist that a new trans cooler and lines and trans computer be installed with the new 3rd transmission, all under the supervision of a factory rep (there could be a wiring harness issue)

Sounds like a "perfect storm" scenario to me, till all ancillary systems that the trans depends on are ruled out as failure contributers, it makes no sense to install a 3rd trans unless one is a 100% sure of the root cause.

I wonder if just the obvious symptons are only being treated i.e. burned slipping clutch disks leads to the easy conclusion tran is defective.

In just one example among many; it could be the controller that cuts pressure at the shift points (along with engine power) in order smooth out shifts with the abnormally high friction clutches used in this design is shorted and not putting the trans back into the proper clutch pressure profile.