If you don't hook up the kickdown cable then the trans thinks it's alway under a low load and backs off on the mainline pressure of the fluid that holds the bands and clutchpacks in place when they are needed.
Low pressure= slip under a load like gettin on it a little and the trans thinks you are just idling around.
End result is fry the bands and clutches.
The kickdown cable (or TV cable) is called "TV cable" for this reason.
Throttle Valve cable.