My plane just came out of annual and I had two items worked on that were of significant note.
1) Motor Mounts- We replaced all front and rear mounts. They weren't really bad, just a little soft, and when you pushed the front and rear prop spinners up and down there was a bit of movement so we decided to replace the mounts. It actually raised the rear engine 1/2" and took virtually all of the mevement out of both engines. In flight the plane seems smoother, quieter and there is less "warbling" during altitude or heading change. It almost doesn't sound like a Skymaster anymore
2) Engine Baffles - The engine baffles were getting old and beat up so I had them all remade. In flight the engine CHT's were below Center Green, and what was most remarkable was that on both engines the bar graphs for all EGT's and CHT's were virtually equalized during all stages of flight (note that I have Gami's) but I have had those for 3 years, and have never seen virtually perfect termperatures.
In summation, just a suggestion to check those two items for possible improvement in your aircraft operation.