My last boat had a 496ho and it was flawless, never missed a beat. That said, I've read quite a number of complaints about sensors and guardian mode with them so don't be too quick to change your 377 because of a couple of electronic gremlins. Top speed sounds a bit slow, tell the experts here your prop size and peak engine revs, it may just need a different prop to get things moving faster. First thing I'd do is make sure you're getting all you can out of the current setup before spending money on an engine change.

My 2 cents, good luck and welcome to OSO.

RR