My advice is to slow down your approach. Standing nearer to the foul line will help. Muscle memory sets in when you stand too far, causing to make bigger steps to reach the foul line. The 3rd and the sliding step is crucial for you to keep low. Here, we called it the "Power Step".
I do not advise slowing your feet down at all. The speed of your feet is dictated by the timing and speed of your armswing. Slowing the feet down without adjusting the armswing will cause you to slow your swing down to match up and kill your ball speed.
If you slow your feet down you will tend to have even cadence to the foul line and lose the power step as all of the steps will be of even size.
The distance you should stand from the foul line is determined by standing with your heels on the dots behind the foul line and taking 5 steps back toward the setee area, the steps should be normal walking steps for a 5 step delivery take 6 steps. Many of you who try this, will find that you should be starting at or in front of the front set of dots. I can't tell you how many people I see that stand at the back of the approach and take only 4 steps. Your steps should be normal walking steps, not giant galloping steps.