I have Livorsi tach and yesterday we were running along and the Tach seemed to be bouncing wildly, will it do that if Im on the rev limiter? (6800 rpm)

Yes it will, but you should be able to hear it also.

The rev limiter will drop cylinders either randomly or in a sequence to prevent high RMS, thus the tach bouncing.

On the back of some tachs is a litte screw that has 4,6,8 on if rotate the screw thru all the position and make sure you reset it on 8 (assuming you have an 8 cylinder).

from the post above it is called the pole adjustment / setting srew,