hi and welcome to the support group -
I have permanent nerve damage in both legs - had EMG and NERVE CONDUCTION TEST done to confirm this - it also shows which discs are affecting the nerve issues.
Have you had this done? If not it may need to be done to check and see what is going on.
Also, to me, your gabapentin dose seems low to treat the issues you have. this med usually starts out on low dose bout 300mg daily then slowly increased until a therapeutic dose has been established. I am now taking 3600 mg daily of gabapentin and it does help with the numbness/tingling/sharp/stabbing/rubber band twinge effects.
A good PHYSIATRIST PAIN MANAGEMENT physician can help with properly treating the pains you are having as they do have numerous treatment options designed for the patient.
http://www.spineuniverse.com/treatments/what-physiatrist I had my back surgery 2/08 Anterior Lumbar Fusion L5-S1 - I fused 100% and bone is growing back. the surgery was a success as the surgeon stated he would fix my disc which he did, however my pains are worse now than before. I have chronic low/mid back pain and the nerve damage in both legs. so I do know what you are going thru.
I don't know how long it's been since you have seen a spine specialist (maybe get different opinions) and see what is going on - a new MRI/CT Scan may need to be done to see what's going on - also seeing the PHYSIATRIST Pain doc too - they can refer you to a good spine specialist.
hope this helps - please keep us posted - take care - Joy