Bob,
If you have a chance, read the info on steps that we have. Under technical, click "common problems" then scroll down to "entry steps". The most common problem is the motor. It always stops in the same location internally. Many repair shops will just replace the motor or even worst sell you a replacement step. Quikkee used to sell the motor & transmission along with the control box but I think since Lippert bought them out I do not know if they offer that anymore.
Seeing that the step has been replaced, you may compare the operating systems of the new with the original step configuration along with the shape and length of the actuating "arm". If similar, reinstall the original and swap the operating system. Caution: The older system used "white magnetic switched" (normally open) and the replacement uses "black magnetic switched" (normally closed). Check the step operation when you are done. If transposed, the step will extend instead of retract when the door is closed. Hope this helps, Fred