727 shifts early

You need to take some weight of the governor valve, or increase the counter spring pressure.
Look it up, it's not hard to do.

Here's an article about it.
http://www.moparmusclemagazine.com/...ft_speeds_on_the_727_torqueflite/viewall.html

I have an easy mod to the kickdown lever that works well except for WOT.
It is mostly for low and midrange shifts, so the governor mod is what you need.