Even though there are no steps with the stage 3 drill, your intention should be to mimic the pressure and force that is applied to the trail leg and the lead leg in stage 1. The stage 1 drill uses steps because it makes it natural and easy to use the force that your legs can generate during a golf swing.
The challenge with stage 3 is to generate a comparable level of ground force with each leg, but without taking any steps.
Naturally, this is a more difficult task, but Stage 1 and Stage 2 should create the neurological and physiological pathways that you need to recreate those force patterns, without taking any steps.
It’s okay if your heels come up off the ground a bit. If anything, this is actually a good thing. It means that you are applying similar levels of pressure to the other stages, but without taking any steps.
Aim For 10 Solid Reps of the Stage 3 Drill