My hand numbness was caused by a combination of 1) downward saddle slope and 2) too-long saddle to bar length. The former caused me to slide forward and carry far too much weight on my hands; the latter moved my torso forward, also placing a higher proportion of my weight on my hands. I'd check your saddle alignment first and go from there: if it's not completely level, fix it and see if that takes care of the problem.