I would first double check the balance point. I bet the MVVS .40 is SEVERAL ounces heavier than the recommended .25 - .30 engine ,and that could easily screw up the flight characteristics. Excess power is OK as long as you practice judicious use of the left stick. What specifically is the plane doing? Is this your first aircraft of this type? They typically are VERY maneuverable and if you have the throws cranked up, the plane may be flying as intended, but your thumbs just aren't up to the task yet. And I don't mean that in a condescending or insulting way......just throwing it out for consideration.

Erik