Kickdown linkage problems
There is an adjustment at the top of the vertical rod coming from the tranny. Screw that top piece out to push the pivot back toward the carb. You should have just slight free play in the rear pivot when it's correct. If it's shifting late the pressure is too high too soon and it will shift late. Some later A-bodies had an adjustable carb rod setup I believe.
I made mine adjustable at the carb using a Lowes turnbuckle and flipping it upside down to clear my taller throttle bracket.:toothy10: