More Qs..... If it's an Optimax, any lights on the dials that might hint it's in "get you home" mode?
Does it sound like it's labouring? (I guess it will have electronic rev. limiting so shouldn't go the other way)
Is the engine secondhand? If so, any idea what it was pushing along before it met your rib? (prrop likely sized for previous job, as mine was)