My 2020 rocks forward and backward upon the first start up in the morning. Thought it had to do with the seat moving, but determined that wasn't the case. Anybody else experience this?

 

Normal. It is cold fluid on the clutch packs. Lots of vehicles do this.

 

Should not do this especially in Summer temps because the trans converter is not engaged to the power train behind it until put in gear.
The only other cause would be the one way Diode is not unlocking from the last time the truck was used.
The old time transmissions did tend to do this but this a 6 or 10 speed should not do it with the ULV very thin fluids.
II you notice, the Engine RPM goes down when putting the Trans in gear as just explained. Then the engine is powering the trans and the valve body has opened a fluid channel to the first Gear path that is ready to move the truck.
You should check to see if there are any Trans codes set.
Good luck.