Its been 4 years with 700R4, no problems. Heavy duty clutch pack. I would ask how you know ?
They are a notoriously shiatty trans...I have smoked 3 personally, they were all "built to the hilt"....my junk definately gets used pretty aggressively. .02 In addition, I have several friends who have attempted to use them in their buggies with exactly zero luck as well....just a really light duty pile imho. I can also tell you that I've broken the tailhousing on two th350's as well, I've figured out that a second rear output brace is a must on them as well. .02 I run a 4l60e in my current Chevota and haven't had issues with it yet...keeping my fingers crossed. I will definately only run a th400 or 80e in future buggies fwiw.