A rear end specialist (uh oh, that's going to go in the wrong direction on this forum).
A differential specialist, (nope can't say that, it's not a differential).
Got it!
A ring and pinion specialist that I know says a new ring and pinion will run hotter than a well broken in one. Seems when new, the contact between the two gears is not always 100% causing localized hot spots. You will probably see lower temps as it breaks in more, but they all get hot. That's probably why Yamaha puts the black stuff (graphite or molybnium)(sp?) in the final drives from the factory, to aid in break in.