Most likely a blown fuse
In 1955, a Cadillac convertible would have typically cost around $4,000 to $5,000, depending on the specific model and any customized features. These prices would be equivalent to roughly $40,000 to $50,000 in today's money when adjusted for inflation.
A fault in the Digital Transmission Range (DTR) sensor will cause those symptoms. It may need to be adjusted or replaced,
Most likely.
insufficient engine output hill acceleration demand (from driver) headwind bad thermostat electrical problem ford
driving it to roughly
Rocker cover gaskets need to be replaced.
Heater coil
kickdown linkage needs adjusted
Assuming nothing is broken, I would change the trans fluid and filter first.
Possibe blown fuse
A bad resistor or a bad switch.