The 1st automatic transmission to implement a torque converter (rather than a fluid coupling) was the Buick Dynaflow, which was released for your 1948 model calendar year. In regular driving, the Dynaflow made use of just the top rated gear, depending on the torque multiplication from the torque convertor at https://zionrtsol.tinyblogging.com/helping-the-others-realize-the-advantages-of-gearbox-auto-77813901