For the past few months, I've been diligently working on my left hand to the point where I am very comfortable using it.

My main problem right now is that I can't make a full speed power move dribbling with my left. Meaning, if I am on a fastbreak, I can't cross over to my left and keep full speed with the left. Or, if my man is pressuring me tightly to my right, I can't blow by him to the left. I can only dribble left at normal speed. I can't go full speed with power.

How can I improve this? Would just running up and down with my left going full speed be enough?