88 regal vibration

Have 88 regal that has vibration at speeds over 34mph.It does not vibrate if accerating quickly. Have replace both half shafts, motor mount, tranny mount is fine, one ball joint. Any ideas?

Forgot to add the vibration goes away when I let off gas. Could it be a bad coil or ecm?

I know it sounds too simple, but you may want to chek your wheels to see if you have thrown a weight. Your tires may need to be rebalanced.

New tires, they were the first thing I checked.

If this started since the tires were replaced have the balance rechecked.

Turns out the vibration was coming from the torque converter, which caused was by lack of power due to a bad ignition module.