Freightliner cascadia shifting issue

The Freightliners with automatic I drove did same thing when hooking to trailer. I believe it has some load sensing stuff on the transmission. It it just needs pulling the trailer to know it’s heavy again. You can put pedal to the floor bobtail and it won’t put crazy power to drive tires. The transmission have performance mode and that will change the shift point so it pulls more. If it’s available you and push the manual/automatic button on the stalk and it will show Performance mode on dash. If you have the pedal on the floor you can try pushing harder and it will click and go a little more to floor and activate Performance mode as long as you keep pedal to floor.