We too have the power step gremlin. I replaced my door switch today and found that it was a straightforward job on or 2006 2551. Here are a few photos if you are considering the job.
Here's what the switch looks like from under the Phoenix. At this point, I was concerned that the switch might be rusted to the frame. I lucked out when the switch pulled out with a reasonable tug.
Loosen the 2 screws that you can see from inside the doorframe and the switch will pull out straight toward you. Yay Phoenix! You do this job sitting in the doorframe rather than lying under the unit. Boy, with
that much rust it was a wonder that it was working at all!
Switch the wires from the old switch to the new, slide the switch back into the doorframe, screw the bracket back to the frame and you are done.
I did kill the house power while doing the repair. I was expecting the power step to come sliding out and bop me in the face at any time, but I survived. Next winter's project; working on that rust. Thanks to everyone on this thread for the info and help and thanks to Phoenix for a straightforward design of the switch.