Manual is the same as automatic on the powershift.
In PRND the
TCM recieves the range (PRND) selected from the transmission range sensor and decides what gear to select.
In M the
TCM recieves up and downshifting orders from the driver over the
CAN bus, if in agreement
TCM will oblige.
In both cases the gear change process is mechanically identical.
If the fluid level is correct and the driveline components are OK, I dunno.