GlennE2

I have a Ssangyong which has a lexus v8 1ufe and auto gearbox. I replaced the ring gear and moved the gearbox back approx 10cm to get access to the ring gear. I assembled and startewd the car. It selected reverse and drove normally for approx 3km. I switched off and started again, just testing, and the car would not select reverse gear nor go into 4 gear once I was driving forward in drive. I am unable to find the problem. Can anyone tell what I have done wrong or where I can start looking?