Rather than changing doctors, why not talk to his current doc about the problem and ask about the addition of a COMT inhibitor to the levodopa/carbidopa (Sinemet).
Adding Comtan (entacapone) which does not cross the blood brain barrier, allows for the inhibition of the enzyme which breaks down dopamine after it is released in the brain.
Some people take it as a single medication known as Stalevo (levodopa/carbidopa/entacapone).
Dr Glass is right on target. Since there is LBD (dementia) the cognitive issues and personality changes may have little or nothing to do with medications and everything to do with alterations in brain chemistry.
Developing a good relationship with a physician is not always easy. Make sure that the doctor is receptive to articles you might bring or to written questions. Usually doctors have an easier time when you bombard them with the written rather than the spoken word.
This might be the time to find things that might calm your Father. Photo albums which you can view together? Music he used to like or music that calms him now. Whatever it might be.
You are going to have to make your peace with having lost some of the Father you knew and loved. This new person may not be a loveable but know that inside that person may still be there.
Aging is not easy for anyone. In a way it is a deconstruction of the person it took us so many years to become.