Prepped boat for use by changing plugs, charging battery, lower unit oil change and then took boat to see how was running. Boat fired up fine and seemed to be running great. Ran near wide open for about 15 minutes when I crossed a series of large waves and the boat came out of water, I throttled down until the waves had passed. When I tried to bring the boat back on plane I could not. The engine seemed to bog down as I opened up the throttle. I could only run at low rpms. If I tried to open up the throttle the engine seemed to want to stall out. So I put the engine in neutral and raised the engine to see if I had a prop problem, I did not. I turned the engine off and checked the battery, it was ok, checked bilge to make sure i wasn't taking on water, Ok. Started the engine again, fired up fine. Proceeded to open up the engine and it did. I got up on plan and headed back to the ramp and the engine ran fine until I throttle down, came off plan and then the engine started the same problem as before. Only capable of running at low rpm and running rough. Was barely able to get boat on trailer and head home. So what do you think could be the problem ?