I have a 94 mustang. When in overdrive around 45-50 mph my car goes into neutral When overdrive is off car runs fine but at high rpm's.What are the possible problems

 

maybe your transmission needs a fluid change obviously somthing is wrong with the tranny get it checked out

 

change fluid and filter

 

Could also be the torque converter or an electrical problem. I would take it to a good shop.

 

I have to say that is a strange problem. I'm trying to think if anything is electric for shifting on that year. I'd take it to a good transmission shop and have them change the fluid and filter and if you can have them flush the transmission at the same time.
That valve body inside the trans could be sticking and not letting it stay in overdrive. But it is something a professional needs to look at. Not a at home job for most of us on here.