The hydro will still work at lower rpm’s and become progressively noisier as rpm increases, if the plates are switched. And eventually destruct.
I would let the oil settle then remove both release valves and slowly pour oil into each port while turning the input shaft by hand. Turn the shaft both rotations while feeding the port that is “sucking”. Reinstall the valves and try it. Do you have auto release valves or button release? Do you have access to other known good valves?
Dumb question, but did you put the pin back in the swash plate and trunion shaft?
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