Transmission not shifting properly

Hi everyone
My transmission in a 67 chrysler newport shifts hard from 1 -2 and doesnt shift until about 23 miles per hour and motor at high rpm. Then from 2 -3 at about 45Mph.
oil level is full. Is there any adjustments? or should i take to transmission shop, Do the newer transmission shops know how to service 727s
thanks i dont want to do any damage.
Author: 67mopar