my pitbull(thor) was abandoned when he was approx. 1year old. a friend found him and gave him to me. he was so malnurished that his gums bled when i gave him a chew toy and his head was bigger than his body. thor suffered severe seperation anxiety.he chewed everything and even destroyed my couch! i took him for long walks in the woods and let him run so that he would get out his energy,i gave him chew toys i also had another dog so thor was not alone.ive had him 5 years and he does not chew anything.hes such a great dog! after a while he knew that i would never abandon him.i think thats what stopped the seperation anxiety was time. i know that is not the case with most dogs but dont forget yours is still a puppy. it sounds like you are doing everything a good dog owner can do. have you talked to a vet for suggestions or ideas? good luck!