Aggressive German Shepherd male

Question
We purchased a 3 year old GSD from a kennel. When we picked him up he was not aggressive at all. On the way home we went by the vet's and got him a rabies shot. We traveled about 2 hours to get home.
We put him in a pen to himself and the next morning when we went out to feed him he was acting crazy as a bat.
He is barking a growling every time we go out to feed him.
We won't get close to him because I know he would attack us.
We called the owner and she said he never acted this way with her.
She suggested that the rabies shot might have had a reverse effect on him. He really does act mad. He does not foam at the mouth but all the other symptoms are there.
We have had him for 8 days now and he is still acting the same way.
We have other GSD about 50 feet away in another pen.
Do you have any info. to help us out.
If we can't tame him we will have to have him put down.
We gave allots of money for this dog and would like to keep him.
But believe me when I say he is acting like a mad dog I really mean it. He will spin around and hit the fence and act as if he could get to you that he would attack you.
We have purchased other GSD at ages 1-3 years old and in about a week they settle in. But this one is not even close.

Answer
I don't like the sounds of this at all.  Have you checked with the vet?  I have never heard of such reaction.  I am not sure what to say.  Perhaps have the former owner come and take him back.  He may have reacted poorly to being shut up by himself in a strange place.  Shepherds don't rehome well.