S-Type 66, Auto trans shifts difficult until warmed up, why?

Hello,
I recently acquired a 1966 S-type Saloon. Until it warms up, it seems to shift with difficulty. Can someone please explain if there needs to be an adjustment or how does this issue get resolved?
Thank you

Bill

Hi Bill welcome to the forums, can you confirm that the car still has the DG box?

I know nothing about auto transmissions but did you check to make sure your trans fluid ( oil) is at the correct level ?