Just installed a brand new 9.9 on a 16' pontoon. Motor runs great, but I am getting a lot of shudder and noise at certain RPMs. I can work around it to some extent by altering the RPMs or slowly increasing/decreasing acceleration, but it's not right. It came with the 10x5 4 blade "high thrust" prop and it seems like the boat of course does not plane out, and as RPMs increase it is spinning out or cavitating maybe? Am I on the right track? Had an older Evinrude on it and never had this problem.