tom, you might be interested in the "Browse Logic" function which hides itself under the "Search" menu....
It gives you a searchable "tree-like" view of the logic, that you can expand interesting-looking branches, and explore the logic along them. (Interesting-looking, in this context, may require that the program has adequate rung comments.)
It only displays the "do", "action", or "output" type instructions for each rung, and that in itself is a great fault-finding tool. You can, from there, choose to go to the actual rung in the logic to see it all.
It's hard to describe the usefulness of it, but it's worth checking it out to see if it helps you.
I've had feedback from people who didn't know it existed, but now use it regularly.