Yup, those Z71 springs are longer, and stiffer than your factory springs on your Yukon. SLT / SLE? Do you have the Nivomats? Sorry, too many threads, and I forgot.. (Nivomats are RPO: ZW7) “Premium Smooth Ride” if you do have them, how many miles on them? Those shocks make up the difference for the smaller, softer springs. They’re honestly pretty amazing in my opinion, for the tech of the day.
ETA: Re-read your first post in the thread. So yes, the factory springs are ZW7, and were not necessarily worn out. They’re made smaller, with less capacity than the standard springs, due to having the self-leveling Nivomats. There is also a 3rd spring option, for the non-nivomats, which would be in-between the capacity and size of the ZW7, and the Z71 springs. So you’ve got another inch or so of height, since you went with the Z71 springs. After purchasing my SLT, with ZW7, I had initially decided to replace mine with standard shocks, and Z71 springs, but ended up changing my mind, and stuck with the Nivomats. I’m very happy with them, just wish they weren’t so expensive to replace.
ETA2: The hose you referred to is the diff vent tube. You shouldn’t have any problem disconnecting it for work on the suspension, just make sure you reattach when you’re done.
ETA3: I’d clean up the rust with a wire wheel if you can get one in there. Guessing you don’t have much room though. Maybe a dremel, to clean it up? If you can manage to get the corrosion off, I’d then clean it with something like denatured alcohol, and once dry, put a good coat of POR15 on it, or even just some black chassis type spray paint.