Great that he's doing so well. You are probably correct about overload, but awesome he did well with it initially. Start watching Jabber's body language for cues when he's had enough. I know because of his size and tail that finding a carrier can be difficult. A friend of mine found a dog crate on the back seat works well for his big boy, also a B&G.. Stopping short can severely injure a bird if they get launched towards the wind shield. Really sounds like Jabber has settled right in to his new home with you and your family, congratulations!