Kayteg, the locking rear axle option is a selectable electronic locker, not just limited slip. Works up to like 30mph then unlocks. It is a great option IMO but for you it would be a waste if you have 4wd since you said you don't even really use 4wd.
I had one on my '13 and it was great on my steep driveway in AK, kept from having to shift to 4wd in the winter and makes a 4x4 a true 3wheel drive, lol.
My '15 is 4wd and no locker. I use 4wd regularly but have not missed the locker here in the PNW. But this is my work truck so no gnarly 4 wheeling in it!