Have you tried lifting weights? There are some movements that activate a lot of muscle groups, yet are low impact as well. Things like seated overhead presses
and bodyweight squats
will help you build muscle, which in turn helps you burn more fat at rest.
There was a point in my life where I didn't do any cardio at all (I think it's incredibly boring) and only lifted weights, and I lost 20 lbs. , so I'm speaking from experience. The step machine may be conditioning your glutes really well but it's really only burning fat for the hour that you're using it. With weights you don't burn much while you're actually at the gym, but you burn TONS more while you're resting and recovering afterwards.