93 starts in reverse?

hi all, I just put a used tranny in a friends Explorer and for some reason it will only start in reverse. The shifter is synced with the tranny as far as the gear selector shows. The reverse lights also come on in park like the neutral safety/reverse light switch is one click off. I did replace the switch but no difference. Has anyone ever seen the cam inside the transmission come loose and put it out of time with the shifter? Any other ideas on what can make this happen?