SOPP469: I worked on Meditation by Vierne and the first page of Vierne Carillon

This question was sent by William, and he writes: “I worked on Meditation by Vierne. And the first page of Vierne Carillon. Very discouraging. Just can’t seem to bring tempos up after practicing. When you practice over and over slowly it is difficult to get pulse of to sound musical. Any thing I can do. Do I just keep going slow? At what point do you move tempo?”