Okay I am going to start over with a play by play of what I did to configure GSX to use the ladder on this plane:
Step 1: Started with a fresh config session
Step 2: I automatically get this screen when I use the Customize button
I have to use the Num 9 key to get (Cycle) the stairs start icon. (See step 3).
Step 3: I will move the stairs start to the top on the ladder in the plane.
Step 4
Step 5: I will move this stairs end to the bottom of the ladder.
Step 6:
Step 7: I have completed the config session by pressing the ("Y") key
Results: