What aircraft and engine are you using? You didn't mention that. You said something about an Eagle that someone else was flying but not your aircraft.

One more thing to check is to see if you have to much throw for the elevator. Follow the instructions in your assembly manual and put only the recommended throw (up and down movement of the elevator and ailerons, and side to side movement of the rudder) in those surfaces. To much will also cause the plane to react a bit wildly. You can set those by using the inside holes on the servo side and the outside holes on the control horn on the control surface.

CGr.