As others have said it may end up being you have one aircraft that is a dog and one that is not.
However I would check the rigging and start at the cable tension on the ailerons.
Sometimes when this has dropped tension they look ok on the ground but in flight the airflow gives in upward deflection. Once tensioned correctly they are flush and match airfoil of the wing.
If you have the upward deflection you may be producing less lift on that section of the wing, correct tension also helps with the old lullaby wing roll on autopilots.