Fixed the swaying issue by torqueing the bolt circled in yellow to spec. There was space in between the bushing from not torqueing correctly. Easy fix.
That's your inner toe rod bolt. Your toe was probably changing while driving and made your rear end feel unstable, especially at highway speeds. May be a good idea to get your alignment checked after torquing this down if you're still on factory toe rods.
I'm having the same exact problem after installing the half shafts. if you notice the driver side half shaft is longer than the passenger side. I believe i put the shafts in opposite of right and left. The DSS box marked RH, which i consider passenger side seems to be wrong or was in the wrong box. if you look up part number: FR33-4K139-BC it's the longer shaft, which came out of my driver's side (LH). I'll update if this solved my issue of the sway.