I had same problem between 65 and 80mph. I had a bad cv axle and lower control arm (leaking oil pressure switch ate up the bushing for lower control arm). I just had Replaced last week both control arms, one cv axle, tie rods, sway bar links,(parts $200

labor $700

new rims & tires balanced and rides great (still haven't gotten it aligned wich it needs)
Price include transmission mount (rear motor mount)
Paid $20 at Firestone to do vehicle inspection
Hope This Helps