In 1956, there was a basic change in the design of the Hydra-Matic. The "Controlled Coupling" Hydramatic was also a 4-speed, like the Dual Range, but its internal parts are way different. The trans was sometimes called the "Jetaway", but that one was also a different design. To the best of my somewhat limited memory, the dual range was only produced for 2 or 3 years, 1953 through 1955, I think. I don't think the controlled coupling trans was ever used in the stovebolt trucks. The CC trans was used from 1956 through 63 or 64, I think, in Olds, Pontiac, Cadillac, and a few Buicks one year, when the Dynaflow plant was damaged in a fire.
Jerry
