question on a flashing OD light on 2000 crown vic p71

The other day I had my crown vic sitting in my drive way idling all the sudden I notice my OD light starts flashing so I shut the vic off then start it back up now I have a check engine light and flashing OD.so I take the car for a spin and notice it is pulling away in second gear and no overdrive. Now I get the car home and wait til the next day to scan it.I wake up the next day go out to the car and start it up NO FLASHING OD but still a check engine light. So I scan the car and get codes po708, po720, po743, po750 then erase codes drive the car all day with no problems until that night flashing OD. Now I replaced the vehicle speed sensor and output speed senor and reset computer and still I get a flashing OD. After replacing the two sensors later that night I have the car idling in my drive way and all the sudden the OD light stops flashing.

Can someone help me with tips on what my next thing that I should try I really dont think the trans is bad it just seems like its something sensor or computer what do you think ??????

Can a neutral safety switch cause this ?? I hear the fords shifter sensor are a common problem