"Efficiency-seeking EV converters should not only avoid automatic transmissions, but also oversized axles, transmission, clutches, or anything that adds weight and reduces efficiency.
Even a manual transmission based drive train will exhibit higher losses when operating at a low fraction of the gear's design maximum torque, which is the normal EV mode." (p. 118)
You should really check out the book. There's a lot more to say about this subject, but it would take pages!
The bottom line is that efficiency is the name of the EV conversion game, and weight is your enemy. Manual is MORE efficient than automatic, unless you can program the automatic transmission to match your electric motor's torque curve exactly.