Attack control

I consistently find that one mouse click results in multiple attacks. i.e. one mouse click will produce two slashes from the same targeting spot. This makes combos impossible to execute since the sequence gets messed up. Any ideas?

Second - So often my attacks seem like I am moving through molasses. They are just unbelievably slow, despite 20 strength, 20 agility, near 20 weapons skills. Again, any tips?

Change the mouse and make sure that it is not broken left button? I had a similar problem recently. It turned out that the left button of my favorite mouse was slightly worn over the years of work and if I did not press the edge of the button, but slightly closer to the middle (as usual lies the hand), the button doubled the click.