[Bill Grissom]

I'm guessing you didn't bother to read my post. Whatever murdered your first catalytic converter will murder the new one. Sounds like you haven't checked the fuel injector wires or looked for the many posts about that with photos. Bad wires could keep an injector spraying all the time, which would pass raw fuel to burn up in the cat. It would also eventually cause cylinder wear.

The way a bad flex-plate could cause this is by messing up the spark timing pickup on the "toner ring" which is welded to the outside of the flex-plate. My car still ran with the flex-plate cracked all the way around and rotated 20 deg, so I doubt that is the problem. It might also cause mis-fire. But much less likely to pass enough unburned fuel to the cat to melt it.