91 4runner, 175000 miles, tranny rebuild 5 years ago, fluid was fine, extra tranny cooler, I run 33's with a Pro-comp lift .................. last week I lost first gear. No noises or anything to make me suspect that something was wrong. Gear just disappeared and OD light flashed.
Turns out the torque converter "blew up". What would cause this? Mangled metal everywhere in the tranny.

-Baffled

 

a few things can cause a converter to implode.
age/fatigue, manufactured defect, overspeed, cavitation (air pocket behind stator or turbine blades causes the fluid to boil and the 'explosion' from the boiling melts pieces of the blades off), corrosion (water contaminated fluid rusts the stator or turbine), or a combination of these.

 

From your post I would guess that the converter weakened from previous overheating ....... before I installed the extra tranny cooler. The tranny still overheated on occasion, but not unless I pushed it. What would be a good way to prevent overheated all together? A re-gear? Not sure, throw suggestions!