when making say 3 double sised copies the machine performs well. the problem comes when doing 5 or more copies then the paper starts to fold in the dulpex unit. i replaced senors and clutches and then ultimately the adu controll board . we have set the duplex registration loop and some otherf settings ..cannot det this machines to do more than 3 double sised without jamming. the adu unit has been rebuilt and swop out with other machine's adu so all our board on our machine is fine...pls help what else must i look for.