trans shift problem

[ike61]

not an a body but drove a friends 57 chrysler 300c 392 hemi to a show last week. I noticed that when it shifted into drive too early. shifted fine, but too early. what could cause this? thanks

 

[TrailBeast]

Probably the same thing that makes most all of them shift too early.
No kit, worn springs and maybe even line pressure issue's.

It could probably be compensated for by lightening the governor weights/valves if not by the linkage.