Plum_Crazy

My boat has twin 496HO's and standard Bravos. I was out running WOT and both engines were turning just below 5K RPM. Suddenly, the Port engine hit the rev limiter. I backed out of the throttles and brought it down to cruise only to find that I had to give the Starboard engine more throttle than normal to keep the engines in sync. At 3500 RPM, the SB stick was about an inch more forward than the Port. Nothing sounded strange and all the gauges looked normal. I had to shift into forward and reverse a lot at the dock and all worked well. I checked both prop hubs at home and they are both good. Drive and engine oil are also normal. What could cause what seemed like slippage?