Motor stumbles at low rpm

[jwolfie001]

This year I purchased a used boat with the 3 liter motor. I am having issues with the motor cutting out and stumbling as I start to rev the engine with it in gear. I can put the hammer down and it gets up and goes but it just doesn't like starting out slow. The problem only exists in gear. No stumbling at all in neutral. Smooth as silk. Any info would be helpful