It could be as simple as the throttle cable snagging on something and holding the slide up a bit. The slide doesn’t need to be up very much at all for a fast idle.
You say you put new cables on, maybe it’s a bit short or it just snags on something now and again.
Maybe coupled with a bad connection in the kill switch.
But if the kill switch is working fine then it does sound like its getting to hot and dieseling.
