Just a short anecdote here...
I'm not sure what manufacturer introduced "lock up converters," but Studebaker began using its self designed automatic featuring a lock up converter for the 1950 model year.
My 1955 President, a hefty 4,200 lb sedan with 259 V8/DG-250 tranny achieved 21/28 mpg in real time road tests in that era. Not bad for a 4 bbl carb, auto and pretty good performance. My uncle used to really rub it in to Chevy/Ford owners...
In a lot of ways, we really haven't advanced much farther.
JT