it can be that you are letting too much weight go onto your hands because you aren't using your core. I also have certain gloves which will leave me with numbness after certain ride lengths. I am slowly weeding out those and replacing them with ones with the right padding. It also depends on the style of the glove, and how the size of that particular brand sits on your hand.
Theoretically you should have enough core strength ( and balance and courage enough) to momentarily take your hands off of the bar while in the riding position and peddaling. So far I can do one and a half hands (one completely off and one ust light fingertips) for a quick count of three.
Recently my trainer has been having all of my free wieght and body weight exercises on a bosu ball, while blindfolded. Great for the balance!
Experiment with some other styles of gloves if you are sure on your seat and posture. Extra core work can't hurt either.
marni
Katy, Texas
Trek Madone 6.5- "Red"
Trek Pilot 5.2- " Bebe"
"easily outrun by a chihuahua."