When I first got the boat, there was a lot of play at the tiller arm/tie rod connections. I overdrilled the holes and made up delrin (plastic) bushings which eliminated all the play.
This spring I noticed a slow recurring vibration which I correlated to the rudders themselves. There's a plastic bushing under the tiller arms where they connect to the rudder posts. If yours is original, there's probably not much left at least on the top. I had play and a distinct "thunk" when I grabbed the top of the rudder post and tried to move it back and forth.
Instead of one bushing, I doubled them up and slightly enlarged the holes so they would fit. Over 2.5 years, the difference doing these two upgrades is amazing. The steering is smooth from lock to lock with zero play.
In the process, I never had the rudder alignment correct. I did it again last week and took it for a WOT run yesterday. I hit 29 MPH and almost 4,500 RPMS! I've never felt the boat go that fast or that smooth. I just changed the throttle cables too which also added to the "smoothness" factor. Yes, I know that the old cables were opening up the carbs all the way

At cruise speed, 2,700 RPMS I was 18.4 MPH which is an increase over my previous runs after switching to 4 blade props. Basically I have driving around with the brakes on since I got the boat.
Take a look at yours, I'm definately finding the speed/economy is a cumulative game. I think I've got mine about as good as it's going to get. I have to get that damn Stb side floscan working accurately so I can post hard numbers but I know I'm using a LOT less gas than last year based on some long runs.
Bob