If it hadn’t done this before, then yeah, I’d say assembly after being taken apart to be cleaned could be the cause.
But the fact is, same thing just happened again that happened in June. Those things require such precision machining that all it takes is to be slightly out of tolerance and the check balls don’t work and boom, you starve the pump and burn up the rest of it.
If it were me, I’d drop the pan one more time. Remove that sucker, put a stock converter with a 5.0 kick down lever in it, button it back up and see what happens. If the stocker fixes the issue, we know it’s in the valve body