For that vintage HR, the proper method for leveling per the manual is
1. slides out
2. air out (releases air from suspension so jacks do not have to extend as far to level the rig - if you don't do this manually before leveling it releases air when you turn key on to activate leveler system)
3. jacks out
When leaving , reverse procedure - jacks up, air up, slides in
Many will argue but if you read the manufacturer's recommendation, this always has slides moving in and out with full air in system and at "ride height"