Hi, thanks for your feedback

Flutter can be heard and seen during fly-by at approx. 3/4 throttle. The airplane is quite heavy, as most warbirds tends to be, so it does not feel much overpowered despite the engine size. This model tends to be tail heavy, so I know some has flown this one with .91 and 1.20 four strokes to avoid putting lead in the nose, but none has reported any flutter. I have checked elevator linkage and eliminated as much play as possible. Feels pretty firm and nice, but there will always be some play unless using high end servos. No gyro here, just going old school
I am a bit clueless. Think the manufacturer must have used a batch of soft balsa for the stab or something. Pulling the covering and sheet as mentioned would be an alternative ,but will add weight as more lead to the nose will be needed to maintain CG.
I am thinking about adding wires between the stab tips and around to stiffen it up??