Since it does not sound like it's overpowered in the modern sense and assuming you don't have too much throw and the controls are stiff enough to resist surface movement then it sure sounds like a CG issue to me.

Bear in mind that there's more to the proper CG placement than the basic 30%. If the tail is too small and the tail moment too short for the wing then it'll require a more forward CG position. Also airfoils with a lot of camber will require larger tails with longer moments or more forward CG's. Not knowing the setup of this particular model all I can do is offer possibilities. But if I'm right and it has a thick'ish flat bottomed airfoil then you may want to try the CG a little more forward. Also if it has strip ailerons try reflexing them up about 5 degrees to decamber the wing a little.

Or were you suffering more from tip stalls and near spins or snap rolls? We are all assuming that it was a pitch problem since you're talking about the CG position.