Hi APJH, Welcome.

IMO, if the gabapentin is not helping the pain, and causing those kinds of side effects, there doesn't seem to be any upside to continuing it, so ask your doctor to wean you off of it (abrubt cessation is not recommended).
http://en.wikipedia.org/wiki/Gabapentin#Withdrawal

Before trying Cymbalta, you might ask your doctor to indulge you and try:
100 mg. Stabilized R-Lipoic Acid (1/day)
500 mg. Acetyl L Carnitine (2/day, 12 hrs. apart)
100 mg. Pantothenic Acid (1/day)

You can take these with the B-12, which should be on an empty stomach.

Cymbalta may help your pain symptoms, but AFAIK, has little/no value in arresting/reversing neuropathy, and has a higher side effects profile.
http://www.ncbi.nlm.nih.gov/pubmedhealth/PMH0000274/

The above combination of OTC supplements may help your pain symptoms (with higher safety and lower side effect profiles) and may help nerve damage as well. If you don't see any results within 30-60 days, you probably won't.

Please feel free to google/check out any/all of this, and more information can be found in the PN Tips, Resources, Supplements & Other Treatments Sub-Forum and in the "Sticky" threads at the top of this forum.

Exercise is important; there's a recent thread on that (and more in the archives). I have similar mobility limitations/cane, but Tai Chi is working for me.

Doc