Are you aware that clicking on the lower part of the GAO cell will give a low velocity and the further up the cell you click will increase the velocity?
Sounds like this might possibly be your problem.
The vol slider you mention is for the global vol level… there is also a vol pot/knob directly above the play button in the pad edit section to control individual pad levels… i generally drop the global level to between -10 and -12db as i find it waaaaaaaaay too hot otherwise.
Hope that helps!