My service manual says the end play is set to zero with the centerlink disconnected, and with the engine idling. Then, it says to preload that sucker 3/8 to 1/2 turn further. That's what it says.
I've never done it that way. I set it with the engine off, centerlink connected,and zero the endplay, then add just a scosh of play.
When adjusting the sector shaft, you have to be very careful to have the steering box exactly centered between the left and right internal stops, and double very careful to not set it up too tight; better it is for it to be a lil loose.
In the center of the box the teeth on sector shaft are a lil further apart (and I think a lil shorter, but might just be wear, IDK). This makes the on-center feel just a lil less sensitive.
If the end play is too tight;
and on the hiway,
then as soon as you turn the steering the slightest bit, the boost control will become active, and you will oversteer. Then because the sector shaft is now loaded, the steering will not want to return to on-center by itself. This results in you chasing the car around from one side of the lane to the other. At 65 mph this gets old in a hurry. Don't be shy to leave some play in there.
