SHIMMY @ 80mph – likely culprits
Check the following in this order:
1) Wheel alignment by a recommended mechanic (dynamic balancing)
2) Check your brake pads!
3) Check thrust arm bushings. (Some call them upper control arms). Bushing can go after several thousand km’s
4) Replace/check tie-rod center, and Left & Right tie-rods
5) Check Struts / Shock absorbers while your there.
6) Sometimes (rarely) disks are warped – replace them (machining is just as expensive if not more).