Hi Mike,
my answer would be to focus on some different steps, one at a time:
a) Use nearly the smallest arc possible (just wide enough to still achieve the desired line speed matching the situation).
b) Move the rod hand as good along a straight path (during the stroke) as possible.
c) When using a medium to long stroke length start the main rotation of the rod during the last part of the stroke. In other words for a back cast: 10, 10, 10, 2 o'clock.
d) Use an abrupt stop. Not too abrupt, but abrupt.
e) Try to cast your forward and your back cast as good along a straight line as possible.
f) Google up the 5 essentials by Bill and Jay Gammel and learn to understand them.
Cheers
Bernd