Note that there are (at least) two kinds of flushing machines: one just exchanges the fluid via the cooler lines, which shouldn't cause any problems, and the other uses air pressure to also "agitate the fluid" and "remove dirt". I think shooting 100# air into your tranny has a reasonable chance of dislodging more than dirt, and that's probably what causes problems. Either that or a "tech" who didn't hook up the machines correctly.

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Prost!