I have never made any rum yet, but a friend of mine makes rum. He said that after running the final spirit run using a pot still (no reflux) and then fast aging it with American white oak, his completed rum just didn't have enough rum flavor as store bought dark rum such as Bacardi Black.
What he has tried with success is adding a little dark molasses to his final rum product. He said that gives the rum more of a store bought dark rum flavor.