Planetaries generally fail because of metal fatigue but running too much horsepower/torque through them can also strip/break them. The builder should have inspected the planetaries for cracks and wear. Not pointing the finger at him but if that is what happened it seems odd that it failed so quickly especially since you didn't even take it out and jump on it. You should have had the trans. in neutral when you broke the cam in because torqueflites don't pump fluid in park (unless a modified manual valve is installed). I can't imagine that would hurt the planetary gear set(s) but it could have scored other parts from lack of lubrication. As for shifting too hard I wouldn't worry about that unless the builder screwed something up but I gotta say that 1st off Trans-go does not sell a "semi manual" shift improver kit. They sell the TF-1, and TF-2 kits which are shift improver kits but they retain fully automatic shifting. The only other kit they have is the TF-3 kit which is full manual shift. And to say he couldn't get it quite perfect doesn't make a lick of sense. To install any of the Trans-go kits it's just a matter of disassembling the valve body, changing a couple springs, drilling 3 or 4 passages, removing a check ball (TF-1 and 2 kits only), possibly eliminating a spring in the front servo, and grinding the throttle pressure valve. Maybe a couple other minor things I'm forgetting but nothing major. I haven't done a TF-3 kit so I'm not sure what is required of it.
Have fun at the Mopar fest.