JV - If your father has nausea and vomiting, sounds like adrenals issues are not being addressed properly. I have no adrenals now - I understand this. It is difficult - too little and you die, too much and well, you destroy your body slowly over time too.
Sad to say, I went to Mayo first and was told to ignore my tumor (which turned out to be tumorS) and while I know they are rated in the magazines to be great in endocrinologly, I have yet to find out which type since everything is wrong with me and they found nothing but put me on thyroid meds.
I know of others who have had similar experiences. It is not a place that is recommended actually. You may want to look at taking him elsewhere - to a university with a pituitary center. Granted, that is still iffy, I was tossed all over but as your dad had surgery already, you should be able to get help now.
You may aslo want to see what their levels of D, ferratin and all the hormones are - all should be checked.
What did his pathology say?