And Vise grips!

What compression are you getting on each cylinder now?

If you had no compression on that cylinder you would have a noticeable loss of torque and about 5-10% loss of top end speed. I would think you would have noticed that last year if it was happening. More than likely the valve stuck over the winter

I bought the boat last year, and didnt run it but a few times before changing springs. My top speed was 69 on gps after having a prop labed by bblades. I saw where people with same set up was getting 71-73