The other possibility is "down thrust" built into the motor/mount. Does it seem to pull down as you increase throttle, or is it a general thing? If during throttle up, then reduce the motor's downthrust a little. If it seems to happen all the time, then it may be the incidence of the horizontal stab or the wing.

If the leading edge of the stab is a bit high, it would result in the plane diving a little. Conversely, if the leading edge of the wing is low, it could result in the same "diving" tendency.
Dennis-