I have one of these kits NIB. This plane would do much, much better with a APC 16x4W than the prop you currently run. Also, just like a profile, it has major control surfaces and lightly loaded therefore, must be flown much slower-I bet that speed and prop were two big factors for your flutter-perhaps servo linkage placement etc. as well. I would not say you are overpowered if throttle managment is used wisely.