we had a very similar probelm with my father. He is taking zoloft. for some reason the docs had halved his dosage and he was much worse. Then improved once put back up to 1 mg. (why they reduced his meds is beyond me)
Also as you might expect --we find my dad has GREAT improvement in dealing with his anger when his fireman friends and other male friends come to see him often . He is better from talking to other people than his caretakers.
For my father his anger is worst at us. With everyone else he expresses that he is doing good and is in good spirits. We try to "schedule" his visits so they don't all come in the same day..
Good luck..
ps I have heard and read that sometimes hospice councelors sometimes work.. check out book "final gifts". there were some truly facinating transformations of anger in there.