When I tighten up one, the other gets loose. The tension screw is turned up as high as it will go but there is too much slack. What can I do to even them out and eliminate the slack before resorting to a complete cable replacement?

I had this issue with my Edge-45 along with the direction indicator being 'off'.

 

I dismounted it from the boat, mounted it to my workbench in the shop...then tore it down (according to MinnKota's manual) and worked on it until

A - The direction indicator lined up with the prop

B - The cables were even with the direction slightly left of center - this lets me turn it to 180 degrees and 'back up' straight

C - Just enough tension to hold it in place without me needing to put a lot of force on it to steer.

 

It's a trial by error process and having it on the workbench made it so much easier to work on it rather than leaving it on the boat.