Another thing to look for is if you use a soft mount, like the Dubro isolation mounts, is that the rubber gromlets are not going soft. I was having trouble with a 3D plane I built a few years back, when I punched full power on the ground, it would snap right and do donuts on the runway. The issue turned out to be that one of the aluminum spools was short by 2.5mm so the motor was basicly setting on a chair with one short leg. As soon as it came up to about 3/4 power, the chair tipped to the short leg, giveing a bunch of right thruts. I'm holdig right rudder, the engine is set for 2 degrees rignt and suddenly there is about 5 degrees of right. What a ride.

Don