The 1220 km/h is about 340 m/s, thus in free fall in vacuum 34 seconds is needed to reach that speed. A vertical fall distance of 5.8 km is required. Thus the module would have to run at least 6 km below ground between stations. Not very pract8ical.
While gravity is used in local train and underground system design, the station is usually built on a hill or at least elevated from ground. Thus this helps accelerating the train leaving a station and decelerating before running into the next station. Thus some energy is saved.
If a new station is required between two original stations (e,g, new housing or other centers) building a new station is sometimes refused, because of the new station would have to be built at the lowest point of the track, requiring extra power to accelerate from the station and extra breaking power is required when arriving to the new station.
If the train can feed the braking power back to the network, the situation is not that bad.
.