They are both used to treat nerve
pain (neuropathic
pain), but gabapentin can be useful in treating other
pain syndromes, like the pain of peripheral neuropathy, or the pain of fibromyalgia.
The only way to know if this medication will help is to try it, but I repeat, it is not used to substitute for opiate treatment, so you will most likely continue your morphine and oxycodone while trying it.
Pain management, like football, is a game of inches.