I'll argue the other side.....
I take 1800mg a day.
I have TN which was bringing agonising attacks of pain that came either when triggered (by cold/by touch/by eating or drinking) or just spontaneously.
I started on 300mg a day (over 3 doses) with the instruction to up my dose every fortnight until I stopped having pain. I was advised to go no higher than 1800.
At 1500 I stopped having spontaneous attacks.
At 1800 I finally stopped having even the triggered attacks.
I still have aches and 'niggling' pains, but no horrid pains. I'm not allowed any higher, but am not pain free.
So, some things require a whacking great dose of gabapentin.
My dad, for example, has been prescribed twie that amount by his pain specialist for his neuropathy.
You COULD consider raising your dose if you are still in pain, but if you are having other side effects then I can understand why you wouldn't want to.