I’d buy that electric one if it was black. I don’t like how far the Ragusa step hangs down in the stowed position.Several iterations of manual as well as automatic entry steps have been created and sold by GMCers over the years. Many used vacuum and others used electric window motors. Some just plugged into sockets bracketed off the frame. But the GMC did not come with one from Pontiac.
In my opinion, the Ragusa Step (https://www.gmcrvparts.com/product-p/rv19.htm) is by far the most elegant and simple entry assist available. Combine that with JR Slaten's Entry Assist Handle and you've got the best solution available. (http://www.gmcmotorhomemarketplace.com/slaten/)
If you've just got to have a fold away step, see https://www.gmcrvparts.com/product-p/gm23-065a.htm.