Gabapentin works very well for many people with CRPS but not for everyone. Before you turn to Vicodin have you considered Lyrica? Lyrica has been shown to be effective in treating neuropathic pain. Here's an article by the RSDA on why it may be effective in RSP or CRPS. According to them it works better than Gabapentin. ( http://www.rsds.org/3/treatment/stacy_campbell_pregabalin_gabapentin.htm). 

Vicodin is a narcotic that lowers the activity of the pain receptors of the brain. It's not the first choice for CRPS sufferers but it is sometimes used and it could be helpful. 

Good luck! It can take a while to learn how to treat CRPS. Don't stint on relaxation therapies such as focused breathing, muscle relaxation, etc. that help to turn down the pain response. They can, in conjunction, with other therapies be very helpful in reducing pain and in cutting down on your medication levels.