It’s all a matter of perspective I guess. Adding it in theory is possible but not even realistic as mentioned. I have a Sierra that is premium plus, and the parking sensors and blind spot are well worth it in Houston. The rear cross traffic alert helped one time when a “wayward” child ran behind my truck backing out at Home Depot due to inattentive parents(don’t even get me started on that).
So what happens when you try it? That would be the only way you would find out. I've never tried it on mine; but yes the switch stays active so you can disable it if you wish. My guess is it would do the same relative to reactivation.
At that weight, it's personal preference. You will be light enough that you do not need to use it. Try it; if it feels more comfortable to you, then go with it. An oversimplification, but essentially what happens is your line pressure is increased to the transmission, engine mapping/throttle is relaxed, and up shifts are longer(allows more rpm, and will hold a gear longer). Downshifts are quicker and more noticeable to increase engine braking.
No grease fittings. I can look up the torque tomorrow, but what you did is fine. A common squeak point is where the leafs actually stack and the pads between them.
There has been an issue with some leaf bolts not up to torque specs, and needing to be tightened. I would check that first. If not, some white lithium grease will help you isolate where it may be coming from.
This was a topic on results from my catch can, and invite others to share theirs. There are other threads dealing with pros, cons, and right or wrong. If y'all want to talk about that, cool. Go have your "who's is bigger" contest in the appropriate thread please.