I am using an incline of level 2, walk at 4.8 - 5.0 and run between 5.8 - 6.6, anything less than that speed for running seems just too slow (I'm only on Wk 2) and actually makes me tired quicker as it's like bouncing on the spot instead of 'moving forward'.
I read that, if using a treadmill, you must use an incline otherwise you do not simulate the 'moving forward' movement and, as a consequence, don't engage the glutes. After I used the incline it did feel a lot more like 'running' as opposed to just 'jogging on the spot'.