Buick LaSabre

Vibrating at 50-55mph, also at 75+, was reduced considerably when forward transmission mount was replaced. Still shimmies and feel little in the steering wheel. Have replaced tie rod ends, back struts and tires. Need help to figure out what I am missing.

Quoting @brett1956 “Have replaced tie rod ends, back struts and tires.”

You’ve replaced the back tires, or am I reading that wrong? What about the front tires?

Has any one re-balanced the tires if two are original? Also have you had the road force balanced? You may have a bent rim, and a road force balance would bring that out.