904 question

Governor blew apart, it happens.
A pressure test will prove it.
Easy fix but a time-consuming PITA, the tail has to come off.

Or TP valve actuator-lever has fallen down. Pressure test will prove it. as will removing the KD linkage-rod off the lever at the trans, and not finding the spring-tension on it that is supposed to be there.
For a guy that knows how to do it, this can be fixed in less than than 30 minutes.
For most of us, the pan has to come off. Still cheap, but PITA.

Neither of these occurrences should ever occur, and especially not in a recently overhauled unit. But yet, that's how they come to me, as recently overhauled units.