Timing Jumping Around

Distributor Shaft collars helps if it is not a timing chain issue.
Check Distributor shaft bushing/bearing for side play.
Is it just a degree back and forth or is it 3 or 4 Degrees.
Be sure weights in Distributor move freely and do not stick if
it is not locked out. You could try a bit more spring tension on
the weights (Bend tabs but not so far that it hit case).
Is it a Mopar or MSD unit?