If the plane climbs power off, it is possibly flying around with "up elevator" to compensate for being NOSE HEAVY. The final approach will remove all doubt as to whether the plane is nose heavy or not, it will want to land fast without much elevator authority. The other possibilites ARE wing / stab incidence / trim related and have nothing to do with the thrust angle if the plane is misbehaving with the power off. Set the plane on a table with the wing at zero degrees [same measurement off the table at the center of the leading edge as it is with the measurement from the table of the trailing edge]. Use a "tri-square" [or similar] to take the measurements. Now do the same with the stab / elevator. You will see if there is an error, the wing and stab cord lines should be parallel with each other. You can at this time remove the prop and bolt a thin straight edge in place of the prop and check the up / down thrust angle....[with your square], it should be very close to 90 degrees.