Why high rpm when changing gears in an automatic when engine is cold?

There are several possible causes. A few:

• The engine is cold and making less power so you are pushing the gas peddle further causing the transmission to hold the gear longer
• The computer is programed to do this ( but I have no idea why it would be)
• The transmission has a sticky or stuck valve that requires the higher speed to move.
• It is really really cold and the oil in the transmission just needs time to loosen up.