In the 60’s I had Chevy Powerglide automatics. They were 2 speeds.
Those old 2 speed powerglides must have had magic in them.
Around 1964, I was riding with a friend in his Impala which had a 300HP 327 and a powerglide. At 65 he stomped it and to my amazement it downshifted and stayed in low til around 75.