Tested the swapped fuel pumps yesterday. Same results for the engines, which rules out fuel delivery.
In my quest to get a more consistent engine sync, I believe it is because the port engine is a little weaker than the starboard engine. To understand what is causing the weakness, I have done the following (with a test run in-between for trouble isolation purposes):
1) trimmed excess sealant in the intake area on the port side.
2) replaced both wear rings and impellers
3) swapped fuel injectors between engines
4) swapped coils between engines
5) swapped spark plugs between engines
6) cleaned both throttle bodies
I'm running out of things to swap. I may try swapping the throttle bodies next.
I'm not concerned about the sync function to the point of worrying about it. I still love the boat and am enjoying it all summer long. I'm just a serial tinkerer and want to understand the sync function better.