[RMcNeal]

I don't think it matters if the trailer is attached to the truck. The important thing is that it is level before opening the slides. If you can get it level while attached, then you should be fine. Also, I would definitely put the jacks down for stability, but not auto-level. The auto-level function causes the nose to dip very low, then back up to level. That wouldn't work when hooked up.