Tiger,try using your lower back muscles to keep your riding position while you loosen your grip on the bars.Lower back strength is essential for long or fast rides.If the numbness is right hand specific,pay attention to your hand/wrist position while your out next time.You may notice that your hand is point up and the bottom of your wrist is pointing down,sort of like a V.That is certainly enough to block the bloodflow to your hands.Try keeping your wrist straight while you're on the highway and see how it feels for you.Good luck.