Originally Posted by Ali Al-Chalabi

I don't think it will store a code. When you press on the gas enough to get some acceleration but not enough to downshift, does the vibration go away? For example, you are going down the road steady at 40mph in gear 5, slowly push the throttle open a little more until there is about a 300 rpm rise, but not far enough to downshift. This rpm rise would be when the torque converter clutch releases, but the transmission should still be in the same gear. Try this and see if the vibration disappears at that point. Again, when the clutch is engaged, it will hold the rpm steady and you will push more, the rpm will be steasy and keep opening the throttle until the rpm suddenly jumps about 300 rpm or so. This sudden jump will be when the lockup clutch releases. At this point the torque converter will be transmitting the driving force and won't transmit the vibrations.

I do not think the problem will cause any damage if it is the torque converter lockup clutch not slipping enough, it will be more of a neusience than anything if this is the problem.