i had my 3.9's put in by herrod and he changed the plastic gear in the auto. it works fine most of the time, however sometimes when u go over 80km/h the car goes into this mode where the over revving occurs. its a intermitt problem. when its in this mode, the trans will hold revs longer and if u boot it, it will hit redline and wont change gear. then it changes back after bout 50 k's of driving. any help appreciated