I know that this might seem a little bit beginer like advice but have you checked the Incodence of both the top and the bottom wing,and also the thrust line of the engine. Cause some of the syptoms you have described could be the incodence being off. After you take off try (at a safe altitude) a hight speed pass and throttle down the engine and see what the plane might do. Course the othere you can only tell with an incodence meter. :thumbup: