Help Please!! ((Liable to get rid of car if not fixed))

1993 Mustang 2.3L 4 cyl. I had just replaced the trans and driove it for like about 21 miles total on the Trans. Was doing 65 mph down a straight road and the car sort of lunged forward and will not longer go into gear. Could someone hel me out on what it is?

Manual or Automatic.

Automatic

probably had trouble shifting, check your tanny fluid, or it just had troube at that speed and going downhill

Well dude....I can shift it, it is just that when it is in anymoving gear it will not move at all. You hit the accelerator and the engine revs and that is it. I can push it freely in any gear except for park. I checked the fluid and the linkage

Looks like you need to bust into it, by the sounds of it.

When was the last time the fuid was changed?