David, first off, welcome to Team Crownline. Sorry for the trouble you're having.
It's possible the 2 situations are unrelated and that you actually sucked some water in thru your exhaust which caused the motor to hydrolock this last time. It could be that the flappers went bad in the exhaust due to the heat although it would normally take you coming off plane rapidly or having a huge load in the back end of the boat to allow water up and in. Remember that the engine temp may have been 220 but the exhaust was much higher. Rubber will melt quickly when the motor is that hot.
It does sound like an impeller problem and at slower speeds, there isn't enough left to provide much water. I hope you didn't blow the head gasket but those temps are up there for a marine engine. Replace the impeller, check the flappers.
O'
"Little Mascara 3"
2003 266BR,496 MAG w/Bravo III