And I definitely feel like this will help me, after a recent ride up to just over 55mph had me worried the bike was gonna slide right out from underneath me.
A G5 shouldn't have any great handling problems. If you feel like the rear end is sliding out from under you, it's more likely the tires.
However, if you think adjusting your shocks would be the answer, just below the notched ring is a notched ramp. The higher you go on the ramp, the more spring preload you have, rendering the shock a stiffer feeling. It will keep the bike from bottoming the suspension as easily, but offers a harsher ride. My dealer initially set mine at the second hardest position, which after riding the bike awhile, I felt was too hard. I backed off a notch to the center one and the bike had a much nicer ride. There has never a been a handling issue due to the shock setting AFAIK on the G5.
GSS's comments were intended for the C5, a totally different animal in the handling department.
I run 24F, 28R psi in my tires.
As for a tool to change the shock setting a pair of ChannelLocks and a rag will suffice. Unless you are doing a of heavy loading and unloading of passengers or cargo, you will probably not find any real reason to ever change your shock setting after you set it where you want it, and even then you can do this at home, you won't really need a spanner in your tool bag. I can think of no situation in which I would change the chock setting on the road. Screwing with that tool box is a pain and not worth the effort for that kind of job IMHO. But then, I'm a minimalist when it comes to carrying excess weight on the bike. I really don't even know what's in the tool kit.
Bare