Do you have a spare prop to put on? That would rule out a couple things. If the current prop is out of balance, has tough to see damage, or not seated properly on the shaft. As for the boat turning left, couple things to check there. Any play in the rudder when you try and move it from under the boat? Should be slight, but not much. What about the little window tab in the rudder? Is it moved all the way to one side? (Bit of a reach here if you have one)

If not the rudder, is there anything causing drag on the port side of the boat? The surf gates are retracted all the way... just thinking of other ways the boat would be turning left. Bunch of weight on the port side?

2 hours ago, ExCCHP said:

Have you been under the boat to have a good look around and push, pull, turn things? Fire it up, put it in gear. Look down the shaft from the back and to the side of the prop. Does everything spin true? 

I would not recommend doing this. Putting it in gear out of the water is a great way to cause damage to your drive line. Specifically the drive shaft seal that is lubed and cooled by water.  

1 hour ago, BigCreek said:

Wow - seems as close to a patent infringement as it could be! I wonder who is stealing from whom. 

It’s all licensing….. 

@ExCCHP  TY.  I have been under the boat and there is zero evidence of any damage.  As far as the pull to the left, I cannot overemphasize that it literally only does it on a deceleration.  It does not pull in the least going forward or during any acceleration.  As far as the vibration, I am going to back it in the water today and rev it up in neutral to see if it still gets the vibration.

I saw there was a acme 2969 in the classifieds that I'm interested in. It's a 17x17 like the 2805 but has more cup. .150 vs .105. I was reading this may increase the low end torque for the hole shot at the expense of more drag on the top end.