I am happy to hear he is doing better for you. Just remember to take it slow and not push yourself or him.
As for the screeching, I ignore Savannah. Do not look or approach his cage. If he makes an acceptable noise, immediately reward him by approaching him and maybe giving him a treat or praising him. Whenever going up to him, say "mommy come here" or another phrase of the sorts so he associates that with you coming towards him. Eventually he will say this when he wants you to come. Savannah knows "come here."
It was funny, I was giving her attention a couple days ago and when I left she said "come here." She repeated it a couple more times when I was going upstairs and when I got to the top she said, "What are you doing?" and she repeated that until I came back down. It really makes me wonder if she knows what it means, or at least knows at what times to say the appropriate phrases.