Printer eject / exit rollers reversing causing jam

My Brother MFC-8710DW Laser printer keeps jamming everytime I try to print. It happens when it reaches the exit rollers and just curls/wrinkles up. I even disassembled the printer to clean the rollers. At first it started working again but began to jam again in the middle of a duplexing print job. At this point I noticed that the eject rollers had reversed direction and this was causing the jam whenever the paper reached the rollers for them to pull the paper through but instead because they were going in wrong direction a jam occurs. If I leave the back cover open I can print everytime and just catch the paper as it comes out the back. Is there a duplex sensor somewhere that could be stuck and it thinks its in duplex mode? Any help is appreciated?