After overhaul or R&R of the transaxle, the transmission
will not get Reverse from Neutral or Park. If the transmission selector is placed in Drive, then quickly moved to Reverse before the gear train spins up, Reverse will work.
The turbine speed sensor and output speed sensor wires are swapped and the TCM is inhibiting Reverse because it is seeing output speed.
Disconnect the turbine speed sensor and see if Reverse returns. If Reverse works correctly, swap the wires the other way.