hi check the wing- to stab incidence. the incidence s/b- 0 degrees- on a bench or ---when standing on tricycle landing gear--the stab- s/b flat-not caring -up or down elevator--are you inputing-up elevator-as the plane accelerates down the runway ? check the c/g- sounds-nose heavy- c/g --s/b aprox. 1/3 the wing cord--good luck---the plane is not rotating on take off-so some down force is being applied to the plane on the runway-and keeping it there- the wing may have some negative incidence-s/b 0 degrees !