HONESTLY, Boston, I'm a 5'8, 110 pound woman and I'm not bragging about that fact because to me that's too thin and it's due to a medical condition, not drugs. I'm solely stating it because you're a guy (probably much bigger then I am) and many think that size matters when it comes to drug useage and I'm living proof that it doesn't.
Anyway, I began at 600 mgs per day and felt NOTHING.
That dose didn't want to make me take less oxycodone and it was as if I was being "tricked" and taking some sort of "placebo" (haha) or better yet, a sugar pill yet I can't even say that because even sugar makes me feel better then a Neurontin...and I WISH it worked like it does for many others

.
I know I told you this before but over a few months span I was jumped up to 4,200 mgs per day. Guess what? Still nothing. 7, 600 mg tablets per day (and I believe my doctor said that that's as high as it can go???) and I not only get no pain relief but I also feel absolutely no different mind or body wise but keep taking them I suppose in hopes that they will eventually help me since much of my pain is caused by a neurological disorder.
The ironic thing is that I heard that it's given in prisons for opiate wds (never been there, hope to never be and therefore haven't witnessed it 1st handedly...just what I heard and never hope to find out as I can't imagine going into wds while in such a place like that as I know many have) and works amazingly for some people for both withdrawals and neurological pain (plus seizures as you stated). But as for seizures Keppra does work better. Do you mind me asking why you take both?
The only reason I asked my last question is because the only medication that has helped my pain even slightly (that's a non opiate) is the muscle relaxer Baclofen. It's even believed to help both alcohol and opiate addictions and wds (and I'm not implying in any way that that's what you would want something for and that's not at all what it's prescribed to me for either). Yet it would be great for many if it is proven to be fully true since it is cheaper then other meds and so much easier to come off of as opposed to other meds. Research is actually even being done by the F.D.A about this now (and I pray no one asks me to share a link to "back up" my statement because I truly don't know how to but would if I could

)
I also want to add that even though it isn't being prescribed to me for wd purposes (just for pain issues), beginning tomorrow (or rather today now) I'm going off of my pain meds so I hope it's true. I'm supposed to take 40 mgs per day yet if I did I wouldn't be able to move so I mostly dose at night since it produces a hardcore (unliked by me) "nod effect". Another thing is that unlike Soma (which is said to be a bit weaker but I've never used it so I can't say) most doctors don't have any problem prescribing it for pain patients since it's also thought to strengthen bones in the vertebra.
Anyway, I'm sorry this is happening to you with the Gabba yet since it once worked could you possibly ask for an increase? The only issue there is that once you get up to the maximum dose...then what

? And you're already taking a lot. I'm not even going to begin to start naming off other meds that I've "heard" have worked (I would only mention ones I've taken) because when someone has gone through pain management they most likely have tried nearly everything so alls I can say to you is that I hope you find something that helps and works (especially long term) which is most often the major issue with nearly all meds.... a doseage increase is often eventually needed.
Goodluck

!!