I didn't believe it myself. Everyone said that you should be able to spin your prop with two fingers. I never could. On my last two boats I always had to use two hands. I figured that was the way it was. I also had a vibration at 2000 rpm, I pulled my prop shaft and it was bent!
After I had the shaft straightened back to .004, replaced cutlass bearings, installed the shaft and believe it or not I could spin it with two fingers! Vibration at 2000 rpm was gone.
I would look towards your prop shaft.