Sorry to hear about your problems.
I was a mechanic at a ford dealer during the beginning of 6.0 and later a field service engineer for ford during the end of 6.0 and beginning of 6.4.
6.4 Is just a 6.0 with extra head bolts to fix head bolt problems, 2 turbos to eliminate variable vanes, and too big a water pump to make up for too small of one in 6.0.
There are reasons that ford sued international and made their own engine.
A piston can be killed by a bad spray pattern from an injector.
tj - if I'm correct in saying that injector pattern was less of an issue with the 7.3, what changed starting with the 6.0 to make this a bigger issue ?
Rgds, D.