You should be as level as possible anytime operating the slides. They, like the fridge can be a little off but needs as much level as you can get to operate smoothly. I always use either shore power or gen, bring in slides and then retract all on jacks. Just my way but my unit is 2011 and has 25,000 on her and still going strong.
Logic will carry you from point A to point B. Imagination will carry you everywhere. "Albert Einstein". 2011 Georgetown 360, Bride of 45yrs, and 2014 Chev Equinox toad, what more could you ask for.