I am by NO means an expert, actually it's likely that I have no idea what I'm talking about. I'll simply share my very limited experience with a similar situation. I've only been "back in the saddle" so to speak for a couple months now. When I bought my bike in June I spent the first couple weeks just riding around my neighborhood and on the paved loop at Flatwoods... I got in a bad habit of resting my palms on the grips and position my thumbs above the grips (basicaly wasn't wrapping my thumbs around the handle grips). I was experiencing the same pins-and-needles you describe, but mine would go away almost immediately after I got off the bike. Now that I am putting more miles in on the off-road trails I have broken that habit and I no longer am having the pins-and-needles problem. I don't know which variable fixed the problem... It seems to me that when I'm on the trails my hands are moving more, whether it be shifting gears, braking, or just shifting weight when absorbing roots/bumps. I think that is a major player in keeping the blood flowing. I would say your suggestion that your body position and/or hand position is probably a good place to start to see if that's the problem.