my suspicions based on what you have would be an issue of weight distribution.
the power step is the last step before your sliding step and its supposed to give you a lot more leverage at that point of time going into the slide,however its not just enough to have power stepping,
your swing momentum,
the first few step approach(how you build up the momentum going into the power step)
and non bowling arm positioning (where its placed from the moment you push out till the finish)
and lastly your release.
however if you are just into power stepping and not be bothered with other aspects of the execution of the power step(which tru my experience is very difficult to achieve without the compliments of other factors),you can try to change the way you approach the power step.
assuming your are a 5 stepper,the 1st 2 steps would be a normal step approach with a heel toe way of walking,the 3rd step would be half a step of your normal step with heel toe approach and the 4th step which is the power step will be just half of your 3rd step (reasoning is for you to get into a power position) with a toe heel approach with the heel as the "digging" factor where you "launched" into the slide with a heel toe approach....where by the sliding step is the longest step of all 5 steps.
this how the power step is being executed as you asked but i hope you understand how its done
but as some others suggested,a video would be able to enhance our understanding of your position to help you better
