I had this issue before i had a 19x11 rear wheel with 325/30/19 Mickey, it started to sway after 60 mph. I switched to Nitto Nt05R 305/35/19 sway was gone. I think its just the tire is to wide and mickeys are softer sidewall so both of those factors play a roll in sway. if Mickeys would be 305 as well might be a different story.