Hil All I can say is that memory problems come from the brain, a part of the central nervous system, and so are not connected to peripheral issues.
I've taken far more gabapentin than your dosage for many years without memory lapses, but what happens to me is not necessarily what happens to you. I suggest you wean yourself off this med and see whether the problem persists. If it doesn't, then gabapentin was likely the culprit.