I do not think that it's adjustable. I would make sure that the petal goes perfectly into the slot @ the kickdown switch. Maybe the switch just needs to be pulled up or something?!
Before my kickdown switch permanently stopped working, it was not doing a prominent click as it should. So your switch still MAY be the culprit. I'd first see if you can align them to make sure they are lining up properly.
Also, maybe your throttle linkage needs to be lubed?