How is the automatic transmission kickdown supposed to function in an 85?

My westy will only kickdown to a lower gear when I push the
accelerator all the way to the floor, and then press even harder, and
even then it's not reliable..  It seems to be more likely to kick
down when cold than warm.  Sometimes it seems that if I back off the
throttle a bit, and THEN stab it really hard, it will finally kick
down.

I've tried adjusting the throttle cable as per bently but I'm not
sure it's making much difference, and it seems like I'm approaching
the end of the adjuster screw.

The temperature thing is weird :  could it be that the cable is just
a little longer when the van is warm and that prevents the kickdown
from operating?

Is there an RPM over which the tranny will not kick down?    I seem
to often get "stuck" at around 2800-3000 rpm in 3rd gear and no
matter of stomping on the accelerator will make it drop to 2nd (which
would put the RPMs around 4000-4500).

Any other things that would prevent kickdown?  Vacuum?  Ambient air
temperature?

Is proper adjustment to have the kickdown happen at the beginning of
the stiffer spring travel in the accelerator pedal travel or at the
very end?

Is the kickdown lever all or nothing, or is there a range of kickdown?