Just work on fun and engagement, and give this boy lots of time, he had a rough beginning! You might also think about changing his name, could be he never learned it, or it could be it has bad memories for him. I think it's cool to try out different names until you find one the dog really responds to, sort like letting them tell you what they like haha! Either way, it often takes a new dog several months to come out of their shell and feel like they're actually home! Congrats on the new pup, he's a handsome boy!
It's not the size of the dog in the fight, it's the size of the fight in the dog. Mark Twain