Thank you for your post.
Standard equiptment on Big Country includes the hydraulic slide system. On Big Country it is a "series" type system. This means that on your 3500RL, the lines run from the pump to the bed slide, kitchen slide, entertainment center slide, and then the main slide with dinette and sofa, then back. When the pump turns on to push the slides out, it adds preasure to all the rams at once, but the slides go out in order of easiest to push out first. This is why your main slide ususally goes out last, bed slide first. When pulling them back in, it is a similar order.
Again, there are other variables such as if your coach is level. If you wanted to apply slide room valve controls, the coach would require more hoses from each ram to the valve, then to the pump. This equiptment is optional on more expensive models like Bighorn, and standard on Landmark. Big Country is plumbed with the simple, effective series system.
I hope this answers your question.