Regardless of what the OEM states of extending SLIDES or not before leveling, YOU ALWAYS DEFLATE THE AIR BAGS FIRST. It is counterproductive to level with the air bags inflated. You also LOSE about 4 inches of leveling stroke, if you do not deflate first. If you do not deflate before leveling(NON air leveling systems), the bags WILL deflate once the jacks hit the ground and start to raise the RV. BUT, you have lost that extra 4 inches of stroke you may need depending on how much stroke the jacks will need to get level. Doug