Shaken not stired plz

[Hawaiian Style]

Something is out of balance! Only when torque converter is locked up and the faster I drive the worse it gets. At 30mph there isn't much vibration but at 70mph it's awfull. If I shift to N it stops so that rules out the tires... could it be the torque converter? Changed the transmission fluid and filter and found more shavings than I would have like to have. I think the tranny might be giving up just looking for any more ideas.

Thanks!

[GSequoia]

Are you lifted? What year, engine, and trans?

[Hawaiian Style]

88 XJ Chief 4.0 auto, 3" lift, installed new leaf springs (full) a year ago. Did notice that the helper spring at the bottom shifted. Hammered it back to center if that means anything.

Like I said it only shakes after the torque converter engages and in a higher gear. Vibrates something fierce at 70mph! When I shift into N at those speeds it stops. Engine is fine, I swapped my road tires for my mud tires and that made no difference. Has to be between the flywheel and the tires.