With regard to the question that was asked...

There is a cable, the Bowden cable, connecting the throttle to the transmission. This cable tells the transmission when to shift based on throttle position.

I don't know how it could have gotten out of adjustment that far all by itself, but who knows?

There is also a vacuum modulator. Its mission is to tell the transmission how firmly to shift. It would not be a factor here.

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2012 E350
2006 Callaway SC560