Automatic transmissions control their shifting by a combination of electronics, mechanical linkage, and hydraulic pressures within the valve body. This is difficult to over ride when converting to an electric motor. Automatics are preprogrammed by their manufacturer to shift at certain points depending on the load to the engine (uphill or not) accelerator position, vehicle speed, and engine rpm. All of these shift points were carefully selected, based on a motor with very specific torque peaks and a specific horsepower band. The torque converter is an integral part of the system, and the torque converter is factored into every calculation.
Electric motors do not need a torque converter, they develop high torque at few PRM's. Electric motors are fairly insensitive to their speed, but do have a "sweet spot" that is about 4000-5000 RPM in many, but variations in manufacturing can change this. Many EV drivers prefer to have a manual transmission so they can leave the trans in second or third or fourth for most driving. (I say second, because my car has a three-speed stick) The favorite gear of most EV drivers is not a direct drive. (unless, or course, you rebuild the differential with a 4:56 ratio or wilder.)
A few folks have built vehicles without a transmission, but this usually does not allow the safety of being able to disconnect the power from the drive wheels in an emergency situation. Without a transmission, reverse is not a problem, the motor can be electrically reversed. Most vehicles need to have a working emergency or parking brake. This takes the place of "park." We do not recommend building a vehicle without a neutral or a means of disconnecting the power from the drive wheels.
