Woodshed as a verb means to me to practice a tough part until you can play it successfully.
Me too. But if it's tough to play at tempo X, I don't see how it gets less tough by attempting to play it faster than X.
Speed up or slow down, it's a simple question:
1. Set the base tempo.
2. Set the number of changes.
3. Set the amount of each change.
All I can get it to do is alternate between original tempo and half original tempo, one playback each. Is that all you can do with it?