Bad gas??

[kkalsch]

Friday we took a trip to Ocracoke Island which is about 70 miles from my marina. The trip there was great. We fueled up at the local marina just before we started our trip home. When we bought the gas I noticed a sign saying 10% ethanol the attendant said they could not get ethanol free gas. Anyway on the trip back we got about 4 miles from the Island when I noticed losing power on the port engine -to the point it took me off plane. The engine never missed or stalled. I brought the boat to an idle and it idled fine no miss.I then shut both engines off and raised the drives to make sure I did not hit something-the props where clear. At this point the boat would not get back on plane- no power at all.So I had 5 passengers and I put them all up in the cabin and got the boat to plane. They came out of the cabin and the boat ran ok however I had to keep the port engine 400rpms higher to keep the engines synchronized (the port engine has always run higher rpm to keep synchronized) for the next 2-1/2 hrs -when we finally came upon a no wake zone -the boat planed like normal and we made it back home.The next morning I only had time to start it up and both engines started and idled normal
so my question is: bad gas? bad knock sensor? or??
The smart-craft alarm never went off
Thanks
KK