I can't see gabapentin bringing on a manic episode at least for me. It is numbing if anything. But everyone is different. I've never heard it used to treat tremors though; it is used mainly to treat nerve pain and off-label for mood stabilization and treatment of akathesia when it is severe and acute.

I've taken propanolol for tremors in the past but after stopping it once and then needing it again later I couldn't be on it because my blood pressure was too low. I think it did help back then (this was from lithium).

I once had a patient's family get upset with me and start screaming at me in a crowded therapy room. I sat and kept talking to them to try to get them to calm down and when they didn't I left the room. A co-worker told me that they proceeded to sit there and later in front of administrators they went on and on about how I was so angry I was shaking. The co-worker had to explain that I had tremors all the time and it had nothing to do with being upset. It was so embarrassing and I've never forgotten it and how much I wished I could cover the tremors at that moment.

I'm sorry you're stuck with this side effect. It's definitely unpleasant.