I agree with Optics Nerd. Please also check Brian's tips, and perhaps describe a little better as to the "character" of the dive on high torque. Is it rolling in sharply (as Brian described)/ Or is it just diving or quickly sinking?
Brian's approach of adding incidence is good, as it will reveal whether this is a bending issue or a torque issue. Last year one of our planes needed twice the decalage as our primary. It flew OK, but this was excess drag in the letdown phase. Without it, the plane would not climb, or would dive at high torque. After Nationals, we experimented with stiffening the motor stick, and problem completely went away. So if increasing the decalage, even by several mm, fixes the climb, look at adding stiffness to the motor stick and see if you can return to design decalage.
Coach, Albuquerque Area Home Schoolers Flying Events
2016 C WS 8th place
2018 B WS 2nd place
2018 C Heli Champion
2019 B ELG 3rd place
2019 C WS Champion
AMA Results: 2 AAHS members qualify for US Jr Team in F1D