Transmission Not Go Into Gear problems of the 2002 BMW 330

While driving, vehicle will not stay in gear. Contacted dealer, cannot duplicate problem. Consumer adds that the transmission will intermittently slip out of second gear while accelerating between 2500 - 4500 rpm. Each time it has occurred, the vehicle accelerates normally in second gear until it reaches approximately 2500 rpm when the vehicle slips out of gear with no input from the driver. Dealership refuses to honor warranty.