I have been having the same problem. I am a bike noob so I never realized it was the bike crippling my left hand until my wife suggested it. Problem for me is that I play guitar semi-professionally and at the beginning of July my pinky on my left hand was not functioning very well. My ring finger was also partially numb all the time. I took 5 days off from bike to give my hands a rest and I bought some Specialized BG gloves to help protect my median nerve in my left hand. I rode 30 miles yesterday and did not get any numbness or tingling on the ride. I made a conscious effort to stretch my left wrist and do resistance stretches at every red light or stop I had to make. I rotated my hand often and forced my rear end further back in the saddle to shift the weight to my core.

My hand feels fine today but I really won't know if I have solved my problem until I ride another couple hundred miles in the next few weeks.