I want to add a little clarity here. The first thing pointed out was the position on the bike. While this is a wise response, it is not the correct response. The responder noting "carpal tunnel syndrome" hit the nail on the head. What you are experiencing is carpal tunnel syndrome. Start from there. Might want to do a little google on that.
Now - back to the positioning on the bike: handlebar reach, saddle position, all that stuff DOES affect how much weight you put on your hands, and contribute to your problem. Better gloves can help, as can more bar-tape padding. I agree with the first responders though, check your positioning first. If you are reasonably smart, you can study up on this and get it pretty close by yourself. But, it is faster and easier to go to a local bike shop with a fitting system. From what you say, you may have already done that. If you got a proper fitting, I would NOT mess with the saddle position to try and fix this problem.
If you still have problems after that, there are plenty of gel padded gloves that might help. Try cork-type handlebar tape if you aren't using that. Or go to the foam-padding type of handlebar wrap if you still need something more. Increasing the strength in your wrists and hands can help, but this is a long-term response. If you had a bike-fit done, you are probably already changing your hand position too. You mention you think the gloves might be contributing. I would say that is a good indicator to try some other gloves.
I don't ride that many miles any more, but back when I did, I used to find that the best I could do was stretch the number of miles before I started having some numbness. After about 75-95 miles with the best setup I had, I would have some temporary loss of feeling. But it always went away shortly after getting off the bike. If it doesn't go away after a very short period of time (minutes, not hours or days), I would think you should still be searching for something to cut the numbness.