I experience this from time to time if I spend to much riding on the 'tops' of my drop bars. It's typically caused by compression of the ulnar nerve in the lower part of the palm and can be particularly an issue for long rides where you aren't varying your hand position much (in the drops, tops of the brake hoods, etc.). Keep experimenting with different gloves as they are a highly individual fit. The gel pads for under the tape work fine, but I've found that just double-wrapping my bars with a good cork-style bar tape works wonders.