We will continue with the investigation tomorrow. According to all your posts, which I appreciate very much, we will definitely compare the propeller pitch, the idle rpm, the trim tab positions, the elevator travel and the other production tolerances. An we will also repeat the stall tests.
This type of airplane does not have a clear stall. According to the regulation the stall is defined as either an uncommanded pitch down or when the elevator reaches the up stop. Since it doesn't have an uncommanded pitch down the stall in this airplane will when the elevator reaches the up stop.
Thank you very much again for your help and I will keep you posted.